"Many new models provide traffic information for free, although there are small ads that may pop up onscreen," said Bartlett.
Then there's voice recognition, which is found on the most expensive GPS units. You can operate menus and enter an address hands-free by speaking a command.
"Our tests found that voice recognition doesn't work well enough to justify the cost," said Bartlett.
But text-to-speech is a low-cost feature worth having. Rather than simply hearing "turn left," you're given the street name as well.
Other good features are reality view, which displays a 3D view of exits and intersections, and lane assist, which shows you the best lane to be in for an upcoming turn.
In the end, Consumer Reports recommends the TomTom One 140-S. It costs around $170, with an optional receiver that allows you to get traffic information.
Almost all of the new smart phones have GPS applications. Consumer Reports' tests find the navigation on some can work just as well as a traditional GPS unit, but the smaller screens can be tough to see and the smaller buttons are harder to use.