Now that the iPhone 6 and iPhone 6 Plus have launched, you may be wondering which new iPhone to buy. Should you buy the 4.7-inch new iPhone 6 when it goes on sale this Friday? Or might the even bigger 5.5-inch iPhone 6 Plus be more suited to your needs? Alternatively you might have an iPhone 5s or iPhone 5c and be wondering whether it's worth updating to the iPhone 6 or iPhone 6 Plus.

If your financial resources are somewhat limited, your decision may be based on just how much of a battering your wallet can take. The iPhone 6 Plus costs even more than the iPhone 6, and that costs more than the iPhone 5s and the iPhone 5c. If you are really strapped for cash that doesn't mean that you can't own an iPhone, there are various places you can get a second hand handset, especially now that people are upgrading to the new models you may be able to get a good deal on one of the older handsets. We'll evaluate all the iPhone handsets here in this article so you know what you are getting for your cash, including whether they will run the latest iPhone software. Most Apple iPhones will still have access to some of the new features coming in iOS 8, which will offer compatibility with some of Apple's older handsets.

Whatever the practical benefits of the new iPhone 6 and iPhone 6 Plus, you will have to weigh up whether those new features, and the frivolity of owning the newest iPhone, are worth the extra expense.

If you have never owned an iPhone because they were too expensive for you it may be possible to join the iPhone world with a relatively new Apple smartphone for less than £350 up front (and potentially for free on a monthly contract). 

You may have never owned an iPhone and be wondering whether to buy an iPhone or a Android or Windows smartphone. We will look at how the Apple iPhones compare to competitor phones from the likes of Samsung and Nokia. We will also look at how owning other Apple products, such as a Mac or an iPad, might enhance your iPhone experience if you purchase one.

How to decide which iPhone to buy

Choosing the best iPhone for your needs depends on how you'll use the phone, which functions you'll want to use most often, and how much you are prepared to pay - although the price is relative as you may find a good deal on a network contract that allows you to spread payments in such a way as to allow you to afford the phone of your dreams. 

To help you decide which iPhone to buy, we’ve summarised the main differences between the various iPhones below, but it’s not quite as simple as weighing up the specs. Every Apple fan is different, and every Apple fan has different priorities. Perhaps you need as many gigabytes as you can get, maybe you are a keen iPhone photographer looking for the best iPhone camera, or perhaps you like to play games on your iPhone and need to make sure that the model you choose is up to the task. We aim to help you buy the best iPhone for you.

A quick history of the Apple iPhone

Before we start, here's a quick iPhone history to put Apple's smartphone in context. Thr first iPhone launched in 2007. Apple actually unveiled it in January 2007, but it didn't launch until the end of June in the US, and November in the UK. The first ever iPhone didn't even offer 3G and it wasn't the first smartphone, but it did reinvent smartphones and pretty soon after all the other mobile manufacturers started producing iPhone-like handsets with touchscreens and apps just like Apple's iPhone.

Apple has introduced a new iPhone (or two new iPhones) every year since 2007. The company has also updated the iPhone operating system - iOS every year around the time the new iPhone launches. This means that anyone who owns an iPhone (or iPad) can update their device and enjoy many of the new features offered by the newest handsets.

What iPhone do you have?

First things first. If you already own an iPhone, which iPhone do you have? This is an important question. If you already own an iPhone it is likely to influence your decision of which iPhone to purchase next. And if you have never owned an iPhone your needs may be influenced by the Android or Windows smartphone that you have been using.

The iPhone models available currently are as follows:

iPhone 6 Plus

The new iPhone 6 Plus is Apple's first phablet-style phone. Phablet is basically the name used for phones that are so big that they are like small tablets. The iPhone 6 Plus has a 5.5-inch screen so it's not a lot smaller than the iPad mini. In addition to the bigger, better screen the Plus offers a better camera than the iPhone 6.

iPhone 6

The iPhone 6 has a bigger screen than the iPhone 5s, 4.7-inch compared to 4-inch. It's also thinner and lighter than the previous year's model and like the iPhone 6 Plus it features a better A8 processor and a NFC chip for mobile payments.

iPhone 5s

This is the iPhone Apple introduced in September 2013. It's available in gold, silver or grey and has a Touch ID button allowing fingerprint scanning for security, rather than the older style home button with a square in the middle. The Touch ID button is the most obvious difference. It uses a Nano-SIM. Apple is now only selling only the 16GB and 32GB models.

iPhone 5c

The iPhone 5c has a polycarbonate (plastic) shell that comes in six bright colours. Apple released iPhone 5c alongside the iPhone 5s in September 2013. On the inside it's pretty similar to the iPhone 5 although the camera is better. It uses a Nano-SIM. Read our comparison review of the iPhone 5s versus the iPhone 5c. This model is now only available in 8GB.

iPhone 5 (currently not on sale)

The iPhone 5 was launched in September 2012 and was the first Apple iPhone with a 4in screen. It was available in 'Slate' or 'Silver'. The iPhone 5s looks similar to the iPhone 5, but the clearest difference between the two iPhones is the home button which has a white square logo in the centre on the older iPhone. It uses a Nano-SIM.

iPhone 4s (currently not on sale)

Apple was, until recently, still offering the iPhone 4s for sale. This phone has a smaller screen than the iPhone 5 (3.5in) but has a similar metallic shell. It uses a Micro-SIM and was launched in October 2011. Read our iPhone 5c versus iPhone 4s review

iPhone 4 (currently not on sale)

The iPhone 4 looks very similar to the iPhone 4s, and like that model it uses a Micro-SIM. The key difference is the number of megapixels offered by the camera. 5MP in the iPhone 4 compared to 8MP in the iPhone 4s. It launched in June 2010.

iPhone 3Gs (currently not on sale)

The iPhone 3Gs was the last of Apple's plastic iPhones (before the company returned to plastic shells for the iPhone 5c). It had a 3MP camera but no front facing camera for FaceTime. Like the 3G, this model came in black or white. It launched in June 2009.

iPhone 3G (currently not on sale)

The iPhone 3G had a 2MP camera and no front facing camera. This model came in black or white. It launched in July 2008.

iPhone (currently not on sale)

Launched in June 2007, the original iPhone had a 2MP camera. The first iPhone was only available in a black plastic finish.

We have a complete run down on every iPhone ever made by Apple here: Which iPhone: Every iPhone compared

Watch our video comparing the iPhone 5s, 5c, 5, 4s, 4 and every iPhone ever made, we'll be creating a similar video including the new iPhone 6 and iPhone 6 Plus.

Which iPhone should you buy?

Having identified the phone you already own, which iPhone would make the best replacement for you?

If you own an iPhone 5s...

Apple’s iPhone evolution usually allows owners to skip a generation without too much worry, but the new bigger screen on the iPhone 6 and iPhone 6 Plus will be a big temptation for iPhone 5s owners. The big question will be whether to go for the iPhone 6, with its 4.7in screen, or the iPhone 6 Plus with its 5.5in screen.

If you really don't feel the need for a bigger screen then there is no harm in skipping a generation. Apple may one day update the iPhone 5s with a faster processor and other features, but keep the same screen size.

If you decide to upgrade your phone you could sell your current iPhone 5s and get a reasonable price for it, which will no doubt help with the cost of the new iPhone.

If you’ve got an iPhone 5c...

If last year you bought the iPhone 5c you would actually see a boost if you updated to the iPhone 5s now, because the processor is faster in that model. There are various other features that the iPhone 5s has that the iPhone 5c doesn't, like the Touch ID fingerprint scanner and a better camera with better photography features. If Apple rebadges the iPhone 5s and makes it cheaper this may be a good option if you won't want to fork out a lot of money for an update. 

However, if you want to upgrade to the new iPhones with their bigger screens then at least if you sell your existing iPhone you should get a reasonably good price for it.

If you’ve got an iPhone 5...

If you are still using an iPhone 5 you may be missing out on 4G, as that model only supports 4G on a few of the UK networks (basically EE). If you are with one of the networks that isn't supported for 4G, O2, Vodafone, for example, faster mobile broadband on the go is a great reason to upgrade. Find out if your network is supported here.

If you’ve got an iPhone 4S...

Upgrading from the iPhone 4s is a no brainer, it’s a 3.5-inch phone for starters, so whether you upgrade to the iPhone 5c, 5s for a 4-inch screen, or the new iPhones with their 4.7-inch or 5.5-inch screens, you will be able to make use of more space for content. The iPhone 5 was 18 percent thinner and 20 percent lighter than the 4S, the iPhone 5s even lighter still. The new iPhones are even thinner, although since they have bigger screens you may notice the extra bulk.

The only reason that you may not wish to upgrade from the iPhone 4s is if you own speakers and other iPhone accessories that use the older iPhone port. With the iPhone 5 Apple introduced the smaller Lightning dock, which means your existing accessories will need an adaptor, which costs £25.

However, we find these days that many of the stereo systems use AirPlay rather than plugging in directly, and we don't really miss our old iPhone accessories.

In terms of iOS 8, bear in mind that the iPhone 4s – will miss out on some of the showier improvements.

If you’ve got an iPhone 4...

If you are still using an iPhone 4 it's a good time to upgrade. Which ever phone you choose will add a bigger screen, thinner chassis and 4G capabilities. The iPhone 4 is well behind both 4S and 5 in its photographic fidelity and has no Siri voice assistant. It’s also about a quarter as fast as the iPhone 5 so imagine how much faster the new iPhone 6 will be.

In terms of iOS 8, bear in mind that the iPhone 4 will not be supported so you will be left behind in terms of new features and other improvements that will come with the new operating system - including new features coming in Mac OS X Yosemite that will make your Mac, iPhone and iPad work together.

If you’ve got an iPhone 3GS or earlier...

A lot of people are still happily using an iPhone 3GS, perhaps they adopted one when a family member updated their iPhone. They have missed out on iOS 7 and will now miss out on iOS 8, so perhaps it's time to update. There is no need to jump right up to the iPhone 6 in this case, the cheaper iPhone 5c may well suit you, and you could probably pick one up for a good price on eBay or similar.

Whatever you update to, you will enjoy a Retina display, a marvel of touchscreen technology with pixels so closely packed they can fool the human eye, and a far cry from the 3GS.

How much should you spend on an iPhone?

We tend to recommend that consumers spend as much money as they can upfront when buying an iPhone. There are a few reasons why. Firstly if you don't get enough GB at the start then you may feel crippled later - there is no way to add more memory at a later date and no SD card slot like you will find on some Android phones.

Remember when you look at the price of the iPhone as offered by Apple that this is the price if you buy the iPhone outright. You don't have to fork out a lot upfront if you sign up for a contract with one of the UK networks. Of course this means that you will have a higher monthly bill than you would if you were only paying for the minutes and data, but for most people who don't have thousands in their rainy day account, this may be the best choice.

We think the best idea is to find a happy medium. Look for a good network contract that means you won't be paying a hell of a lot over time. Always times the monthly bill by 24 if it's a two year contract or 12 if it's a one year contract and add the up front cost to see what kind of a deal you are signing up for. It may look like a good deal, but it is all relative.

The phones that Apple sells currently are priced as follows on Apple's website, although as we keep saying, these are unlocked, non-contract prices, so you can spread payments over two years if you want to sign up with a network.

iPhone 5c: 8GB, £319

iPhone 5s: 16GB, £459 | 32GB, £499

iPhone 6: 16GB, £539 | 64GB, £619 | 128GB, £699

iPhone 6 Plus: 16GB, £619 | 64GB, £699 | 128GB, £789

What is the best screen size for an iPhone?

There are three different screen sizes of iPhone available currently: 4-inch, 4.7-inch and 5.5-inch. That's a far cry from Apple's insistance that it wouldn't make an iPhone with a bigger screen because of "tradeoffs in screen quality", and because it is less comfortable and ergonomic to use a bigger screen. (Apple has previously emphasised the fact that the 4in screen is ideal because you can use it one handed).

Both of the new iPhones are larger than the 4-inch screen on last year's flagship iPhone, but Apple has made sure that the new iPhones are still comfortable to use despite the bigger surface area. For example, to compensate for the larger screen sizes, Apple's engineers have implemented a feature called Reachability. Reachability is activated by a double-touch on the Home button and it shrinks the user interface towards the bottom of the phone and closer to your thumb. This makes it easier to tap objects near the top of the screen while using one hand.

iOS 8 has also been designed to take advantage of the larger screens so, for example, the keyboard on the Plus has extra keys, including dedicated virtual buttons for cut, copy and paste. And, also on the Plus, apps like Messaging, Email, and Calendar use a split mode to show you more information.

Which iPhone has the best display?

iPhone 6 Plus has a 1920-x-1080-pixel 5.5-inch LED-backlit display offering 401 pixels per inch.

The iPhone 6, on the other hand, offers a 1334-x-750-pixel LED-backlit display. Despite the fact that the display measures 4.7-inch, it works out to 326 pixels per inch, which is the same as the iPhone 5 and 5s.

Apple calls these new iPhones Retina HD display even though only the Plus offers a greater number of pixels per inch. in fact it offers two million pixels in total, that's nearly a million more pixels than the iPhone 6. However, both the new displays feature an LCD with dual-domain pixels for improved viewing angles and a substantially higher contrast ratio, so the iPhone 6 screen is still better than the iPhone 5s.

It's the contrast ratio that provides the biggest difference: last year's flagship iPhone 5s had an 800:1 ratio. This year the iPhone 6 has a 1400:1 ratio, and the larger 6 Plus offers 1300:1.

The iPhone 6 Plus offers 88% more viewing area and three times the pixels on iPhone 5/5s.

It sounds impressive, but remember, while the iPhone 6 Plus packs a million more pixels into the display, but there comes a point where we can't actually distinguish any difference - these displays are referred to as Retina Displays because there are only so many pixels your eye can see.

How many GB is best for an iPhone? What capacity iPhone to buy

Prior to the launch of the iPhone 6, iPhones tended to come in 16GB and 32GB versions, with a 64GB version available for the top of the range model. Apple has also been known to offer an 8GB on the most affordable iPhone.

The current line up is slightly different:

The iPhone 6 and iPhone 6 Plus are available in 16GB, 64GB, and 128GB.

The iPhone 5s comes in 16GB and 32GB.

And the iPhone 5c comes in 8GB.

How do you decide how many gigabytes are necessary?

Apps are getting larger, and photos and videos are addictive to shoot and gobble up and ever-increasing amount of gigabytes. For that reason, as we mention above, we would always recommend going for as many GB as you can afford.

If you already have an iPhone check how much space all your apps and data are eating up on your by looking at Settings > General > Usage.

You don't have to transfer every app to your new iPhone though. We went from a 64GB to a 16GB without too much stress because we culled our apps. You can always download an app again at a later date, Apple knows that you already bought it so you can download it again for free.

Then again maintaining 16GB of space requires a lot of housekeeping, so if you take a lot of photos, or download video from iTunes or iPlayer, expect to fill up the space available quickly.

Given the choice we'd opt for 32GB over 16GB, and to be honest, we think that 64GB is overkill, but for some it may still not be enough, and they are the people who will be pleased with the option of a 128GB iPhone. We think that the 8GB for the iPhone 5c is too small - we'd recommend looking for a second hand iPhone 5c with at least 16GB or 32GB as we think that it would be very difficult to manage with just 8GB given that iOS would take up a significant part of that space.

Which iPhone is lightest? Weight and dimensions of Apple's iPhones

The larger screen obviously means a larger size and a bit more weight, so if you are looking for a lighter phone the 5.5-inch iPhone may not be the one for you. Similarly, if you have small hands you may find that the iPhone 6 Plus is too large to be held comfortably in your hand.

The weight and dimensions of the full range of iPhones currently on sale from Apple is as follows:

iPhone 6 Plus: 158.1 mm x 77.8 mm x 7.1 mm x 172 grams

iPhone 6: 138.1 mm x 67.0 mm x 6.9 mm | 129 grams

iPhone 5s: 123.8 mm x 58.6 mm x 7.6 mm | 112 grams

iPhone 5c: 124.4 mm x 59.2 mm x 8.97 mm | 132 grams

If portability is the key, and if you already own a tablet or use a traditional computer for everyday tasks you may not need a bigger screen iPhone.

Even if you could use a bigger screen you may not need the iPhone 6 Plus - the iPhone 6 screen is still 38% larger than the iPhone 5.

iPhone colours: Which iPhone offers the best colour choices

The iPhone 6, iPhone 6 Plus and the iPhone 5s all offer the same colour choices - silver, gold and space gray.

Only the iPhone 5c comes in bright colour choices. Choose from white, pink, yellow, blue and green.

Which iPhone is best for software?

iOS 8 will work on the latest iPhones including the iPhone 5s, 5c, 5 and iPhone 4s as well as the new iPhone 6 and iPhone 6 Plus (obviously). Read about which iPhones will run iOS 8 here.

There are various new features coming in iOS 8 which will enhance existing iPhones as well as the new iPhones. We're particularly excited about Continuity, Widgets, new tools in Mail and Messages, the new keyboard features. Read more about what you can expect from iOS 8 here: iOS 8 beta review.

If you’re excited by iOS 8 but you’re willing to sacrifice a few features the iPhone 4s might be ok, but you need to keep in mind that that phone will be able to utilise many of the new features to their full potential and installing the new software may render your phone slower and less responsive. (Read about why Apple isn't making your iPhone slower on purpose)

It can be a whole lot worse than the iPhone 4s software situation though. Many of the features that came with iOS 6 back in 2012 don't even work with the iPhone 4. The main things missing are Siri, FaceTime over 3G, Flyover and turn-by-turn navigation. That phone won't even run iOS 8. 

You can also expect some of the older iPhones not to offer support for newer apps. Developers are currently focusing efforts on four-inch iPhones, and we expect that they will focus their attention on the screen size of the new iPhones when those launch.

Which iPhone is best for photography?

None of today’s cameraphones can replace a digital SLR for top-level photography, but iPhones are definitely getting better in this area. Over the iOS iterations we've gained a panoramic shooting mode, burst mode, slow-mo video recording, and various editing features. There are even more new camera features coming with iOS 8. Read about the best new camera features coming in iOS 8.

The iPhone 5s, iPhone 5c and iPhone 5 all offer 8 megapixels. There were rumours that the new iPhones would offer more megapixels but they don't. Find out why that doesn't matter and why megapixels aren’t everything, as we explain in this article: Why it doesn't matter how many megapixels your iPhone has.

What the new iPhones do offer is improvements in the camera software. The iPhone 6 Plus features a camera with optical stabilization, which should help in taking pictures and video. While the iPhone 6 offers an improved camera with digital stabilization.

When Apple launched the iPhone 5s they made much of the fact that sensor size is more important than the number of megapixels. When Apple launched that iPhone, rather than make the pixels smaller in order to increase the amount of pixels that can be fitted on the sensor, Apple increased pixel size to 1.5µm (from 1.4µm – those measurements are in micrometers) and kept the pixel count the same by using a 15% larger sensor. The new iPhones also offer these bigger pixels for better pictures.

Another new feature in the iPhone 5s was a True Tone Flash which was designed to make flash photography more flattering.

Which iPhone is best for battery life

The iPhone 6 Plus model has a larger battery than any other iPhone which means Apple can claim a talk time of up to 24 hours on 3G and a standby time of 16 days compared to the iPhone 6's 14 hours and 10-day standby.

Video and audio playback as well as internet use is listed as 14, 80 and 12 hours on the Plus; 11, 50, and 10 hours on the 6. if you spend a lot of time using your phone to read, surf or check email and Facebook, the larger screen and longer battery life are a better option.

Which iPhone is best for watching movies on the go?

For film fans, we recommend the iPhone 5, 5c or 5s because the widescreen display is ideal for a mini-cinematic experience. The older iPhones with their smaller displays don't suit widescreen viewing very well.

However, the new iPhone 6 or iPhone 6 Plus have dimensions that are even better suited to movie viewing.

Bear in mind that movies will quickly fill up storage, so the 64GB and 128GB models are probably worth the extra investment.

Which iPhone is best for mobile games

This one depends on what kind of games you like. If processor-intensive graphical feasts like Infinity Blade are your thing – and if you intend to keep playing the latest games in the future – then the faster A8 processor with 64-bit support in the iPhone 6 and iPhone 6 Plus - will be worth the price of admission.

However the A7 chip in the iPhone 5s is no slouch when it comes to gaming.

The App Store will contain games that run only on the iPhone 5s or even newer iOS hardware. If you love to play the newest, best-of-breed games, you may well miss out on those titles - or at least their full feature-set and performance abilities - unless you upgrade to Apple's top-of-the-line phone.

Our experience suggests that at least 32GB of storage is advisable for heavy gamers, although you can get by with less if you’re willing to focus on a few games at a time, and uninstall them once you’re finished. 

Read our best iPhone and iPad games feature.

Which iPhone is best for business users

Unless you’re desperate to show off the latest iPhone while networking, or are big fans of gaming and movies in their spare time, business users can probably get by with an earlier model; a super-fast processor will be wasted if your principal needs are email, contacts management and light browsing. 

There are some handy features on later iPhone models, such as the ability to make FaceTime calls over 3G and videoconference when outside Wi-Fi range: a handy option for the business-inclined.

Which iPhone is best for sporty types

If you already own a fitness monitor, or you are thinking of buying the Apple Watch (read: Apple Watch rumours, release date & images and our Apple Watch first look review), you may want to stick with an iPhone 5s or later. Apple introduced the M7 "motion coprocessor" chip with the iPhone 5s in 2013 and this chip works in sequence with a fitness monitor to track the data without over using the battery in your iPhone.