Following the disappearance of Sony, Navman and ViaMichelin, only a handful of brands are currently left competing in the sat nav market—but that doesn't mean you're no longer spoilt for choice!
Don't ignore the cheapest models
The most basic GPS untis make do with a 3.5'' (8.9 cm) screen and maps limited to a single country.
If they do offer live traffic information, then it's restricted to only the most important highways with little coverage of minor roads or town centres.
In any case, such systems aren't as helpful as the marketing would have you believe! Too many areas remain outside of the coverage area, and a lot of work remains to be done.
Despite lacking these systems, the cheapest sat navs are perfectly able to fulfil their primary function of getting you from A to B, as they're essentially based on the same software found in more advance models.
When it comes to the voice instructions your sat nav gives you, one feature to look out for is Text-to-Speech voice synthesis. While almost all GPS systems can give voice instructions like 'Turn right in 100 yards', they usually can't handle the names of streets and towns. Text-to-Speech allows them to give clear directions like 'Turn left onto Banbury Road', a much more natural way of getting round town.
On the subject of making these systems a little more realistic, that's partly the aim of TomTom's iQ Routes system. This suggests different routes depending on the time of day based on journey times measured in real life, not just the theoretical average speed on the roads you travel.