All-in-one PCs offer a convenient halfway house between a laptop and a desktop PC, offering great space-saving advantages but also offering a big-screen which can also be used as an entertainment centre – perhaps to replace your TV. Here's our all-in-one PC buying advice.

Below we've reviewed six very different all-in-ones with unique strengths and weaknesses, and you can check out our most recent all-in-one PCs group test, but first let's look at some general All-in-one PC buying advice.

All-in-one PCs buying advice

Choosing an all-in-one PC is about more than performance. Often used as family multimedia entertainment system, it can be treated much like a TV and will therefore be subject to the same aesthetic considerations as any other entertainment system you install in the home.

Many Windows AIO PCs incorporate Blu-ray players and TV tuners and come with remote controls. They often incorporate a touchscreen interface, with the idea of freeing you entirely from the mouse and keyboard until they're needed.

Windows 7 incorporates multi-touch control as standard, so you can try navigating your way around the operating system if you need to. However, don't expect to have much fun jabbing away at the standard Windows 7 interface. Windows Media Center, on the other hand, is more usable by finger or remote control than a keyboard and mouse.

All-in-on PCMost all-in-one vendors also add their own software to help keep you away from the ill-suited Windows desktop, making the interface more touch-friendly.

Windows 8 is able to make much greater use of touch input, but places more stringent requirements on the touch interface if it is to be certified. Most touchscreen PCs will work, but because many gestures involve swiping the finger in from off the side of the screen, raised bezels get in the way. It's also a requirement that at least five touch points are recognised, so those systems which support only two points (of which there are many) will struggle.

Of the systems reviewed below, only the Lenovo IdeaCentre A720 meets both of these requirements, although no Windows 8 compatibility is claimed for even this system. With few good standalone touchscreens available, a suitably-specced all-in-one PC may be the best way to get a touchscreen PC now which will deliver in Windows 8.

As with any display or TV, you should also consider the screen size you need. Larger screens are more expensive but provide a better viewing experience for multiple viewers. In many cases, all-in-one PCs support HDMI inputs so you can plug in a set-top box or games console. You also get HDMI outputs to set up dual-screens to boost work productivity or connect a projector.

All the systems in our group include full-HD (1080p) or better screens. Look out for a Blu-ray drive to take advantage of these high-res panels when watching films.

With all their components crammed into a thin housing, all-in-one systems must make compromises between performance and noisy cooling. To cut down on heat and power consumption, some machines use low-power processors such as the Intel Core i5-3450S or mobile processors like the Intel Core i7-3610QM. These PCs are generally much quieter to use and these latest third-generation Intel processors pack more than enough power for the vast majority of users.

All-in-on PCWatch out for systems using standard desktop chips like the Core i5-3570K. Powerful as they are, the level of cooling required can often result in an unpleasantly noisy PC.

Due to space and cooling constraints, all-in-one systems rarely offer strong gaming performance. With modern Ivy Bridge processors, there's enough graphics power built-in for multimedia and even low-level gaming. In many cases there's now no need to pay for discrete graphics.

However, most of the systems here incorporate a mobile nVidia chip to give graphics a performance boost. PC Specialist's system uses a desktop graphics card, which gives considerably faster gaming frame rates but is particularly noisy and for keen gamers only.

All-in-one PCs aren't all about fun and games. If you're a designer working from home who needs workstation-level performance, reliability and service, take a look at HP's unique Z1 workstation.

All-in-one PC reviews

All-in-one PCHere are reviews of a range of all-in-one PCs, with screen sizes from 21.5in to 27in, and prices starting from £799.

All-in-one PCs: The iMac challenge

Apple iMacThe resurgent popularity in all-in-one computers can be traced to Apple's long-running iMac. It's evolved from the classic Bondi Blue model of 1998 to the flatscreen form that's now being emulated by other PC vendors, and comes in either 21.5in or 27in screen sizes.

Apple's iconic all-in-one still offers the finest balance of high-grade IPS screens like that in the HP Z1 workstation, along with peerless build quality and cool, quiet operation. Prices start at £999 for the Apple iMac 21.5in model we tested late last year, or £1399 for the entry-level 27in Apple iMac 27in (Mid-2011) 2.7GHz Core i5 we tested in March.

All iMacs sport quad-core processors and discrete graphics, although the range has yet to be upgraded with Ivy Bridge processors and USB 3.0 ports – a new range is expected imminently.

NEXT PAGE: All-in-one PC buying advice conclusion, and how we test >>

All-in-one PC buying advice: Conclusion

If your all-in-one PC is for use in the home, perhaps as a lounge entertainment centre, appearance can be crucially important. In terms of sheer aesthetics, Lenovo's IdeaCentre A720 is streets ahead of Windows competition. It may cost more but many will find it worth the extra for design alone. It incorporates one of the largest screens, incorporating superior panel technology and a frameless 10-point touchscreen which gives it a headstart if you're considering Windows 8. It also comes with great pre-installed software, all making it our Best Buy system.

For serious work, HP's 27in Z1 workstation is in a class of its own. Most will find it prohibitively expensive, but for those who require the ultimate reliability and easy maintenance, it can't be beaten – most core components can be swapped out without tools. It has no touchscreen, but it's the only PC here with a professional-grade display. You'll also be able to rely on a three-year on-site warranty with guaranteed next-day service.

The Asus ET2411INTI is a good mid-range system which retains a high-level of build quality in a smaller, 24in package. It delivers good all-round-performance and friendly pre-installed software which enables you to try a touchscreen environment today, although it won't be so usable under Windows 8.

For the budget conscious, MSI's Wind Top AE2281G is the least expensive of the bunch yet still retains a decent level of performance. You'll have to make do with a smaller screen and forego the Blu-ray player. It too comes pre-installed with software designed for home users.

If you prefer to install your own software and would rather have a more configurable or upgradable system you could go for one of the options from Chillblast or PC Specialist, who have taken a pre-built housings and added their own components.

Build quality suffers with these PCs, which have a distinctly DIY feel to them, but they also use many standard PC components so can to some extent be user-upgraded like a regular desktop PC.

Lenovo IdeaCentre A720

All-in-one PCs: How we test

All-in-one PC: Application performance

Core system performance is measured using WorldBench 6. This customised test suite runs several desktop Windows applications with real-world workloads, mimicking how PCs are used on a daily basis.

These workloads include tasks such as editing documents and images, compressing files, browsing the web and encoding video. Some tasks are then run simultaneously to form an additional test of the PC's multitasking capabilities.

In total, eight applications are used: Adobe Photoshop Creative Suite 2.0, AutoDesk 3ds Max 8.0, Firefox 2.0, Microsoft Office 2003, Microsoft Windows Media Encoder 9.0, Nero 7.0 Ultra Edition, Roxio ViewWave Movie Creator 1.5 and WinZip Computing WinZip 10.0.

Results from 10 individual tests are combined and weighted to produce a numerical score relative to a baseline PC.

Our baseline configuration runs a 2.4GHz Core 2 Duo E6600 processor, 2GB of DDR2 RAM, an nVidia GeForce 7900 GS graphics card, twin Western Digital Caviar WD3200KS hard drives in a striped Raid array, and Windows Vista Home Premium 32bit. This PC scored 100 points in WorldBench 6.

All-in-one PC: Transcoding performance

We set each PC the task of converting a batch of 1080p Mpeg4 video clips for use on the iPad 2 and recorded how long it took to complete. We used CyberLink's MediaEspresso software.

This software is able to make use of hardware-accelerated decoding and encoding built into graphic cards and CPUs with integrated graphics-processing capabilities. These techniques can often shorten conversion times by a factor of 10. Multiple CPU threads are also fully exploited, allowing quad-core CPUs to shine when compared to dual-core versions.

All-in-one PC: Power consumption

Unlike most desktop machines, all-in-one computers may often be left switched on for extended periods. We measure power consumption when idle and when running the CyberLink MediaEspresso test with the display panel set to the default brightness.

All-in-one PC: Gaming performance

These PCs aren't designed for gamers, but we run two tests using Crysis, which still has the power to stretch modern graphics to the limit.

We've included a 720p Crysis test to give PCs running integrated graphics processors a chance. For those with discrete chips we crank up the resolution to 1080p, set the quality to Very High and use 16x anti-aliasing.

All-in-one PC: Display quality

We use a Datacolor Spyder4 calibrator to measure colour gamut and accuracy, contrast and uniformity across the surface of the screen. We also take into account the viewing angles afforded by the display technology each panel uses. We have produced an score out of five each for accurate and uniform brightness and colour reproduction.

All-in-one PC: Subjective assessment

It's not all about speed. We also pay close attention to the physical characteristics of each all-in-one PC, its noise output and build-quality, and take note of important features such as the quality of components.

All-in-one PC: Support

Differences in warranty terms can have a big effect on our verdict. Longer warranties are better, but we also look at the terms and conditions – specifically, whether faulty systems must be returned to the vendor at your own cost, and whether parts, labour or both are included.