The Insider: It's a buyer's market in mobile sound and vision

Everyone seems to have a digital music player these days. Whether out walking the streets, travelling on public transport, or sitting in the car, the odds are that people will be listening to music on MP3 or MP4 players.

But if you're in the market for a new one – or the digital music revolution has passed you by until now – what should you buy? While iPods (and more recently iPhones) have maintained their position among the most sought-after gadgets, there are plenty of brands other than Apple. And many of the newest devices are much cheaper than iPods, while still being competitive in terms of functionality.

Perhaps the first decision to make is whether to go for an MP3 or an MP4 player. The basic difference is that MP4 devices play video as well as music, while MP3 players just play music. Although you might not feel you need a device that plays video, many MP4 players also have touch-screen technology, which makes them easier to use.

If you can live without touch screens and video capability, there are some great devices in the MP3 market at very low prices. In its latest survey of digital music players, Which?, the consumer group, picked out the Philips SA2820 as the best all-round device on the market – and it costs just £20. Although it has a memory of only 2GB, it has a remarkable battery life of 44.5 hours, more than any other MP3 or MP4 player on the market.

Although the cheapest MP4 players are available for as little as £35, you should be ready to spend £90 or £100 if you want a machine with good sound and video quality and good battery life, and which is easy to use.

The Sony NWZ-A828 came top in Which?'s survey of these devices. It has 8GB of memory and a battery life of more than 40 hours, and costs £160. If you want one that has an FM radio as well, you might consider the Creative Zen, which has 32GB of memory.

At the bottom of the pile, you could pick up a Sumvision ICE 1000 for £35. Although it has a radio and a touch screen, its audio-visual quality is poor and it has a battery life of only 11.5 hours for music.

Finally, before you decide on which model to buy, make sure it's compatible with your computer. All MP3/MP4 players are compatible with PCs, but not all of them work with Macs.

Where to buy

As ever, online shopping comparison sites such as pricerunner.co.uk, kelkoo.co.uk and froogle.co.uk are a great way to find the model you want at the lowest price. Individual retailers that tend to offer good deals on these devices include Tesco and Argos, with the best bargains often found on their websites.

Amazon.co.uk is also worth exploring. It has Which?'s best buy – the Sony NWZ-A828 – for £129.99, £30 below its recommended retail price. And you can find this model for under £100 if you buy via Amazon's private sales side; just click on Used and New to see who's selling at what price. But be careful to check that the seller has a good reputation with other users.

What to look out for

How much memory does it have? As a rule of thumb, you will fit about 220 songs on to a player with 1GB of memory.

What's the battery life? Some devices can keep on playing music for more than 40 hours, while others struggle to manage 10 hours.

PC or Mac? All devices tend to work with PCs, but not all work with Macs.

Does it have a radio? Some players come with a built-in FM radio.

Is there a touch screen? Most MP4 players have touch screens, which tend to make them easier to use. They look more hip, too.

The Insider is written in conjunction with the consumer group Which?. For more information on the best MP3 and MP4 players – or to read other product reports – visit their website, www.which.co.uk. To get three issues of 'Which?' magazine for £3, call 01992 822 800 and quote INADVICE