How big should you go? For years, 4.3-inch GPS screens were the standard. Now, most car GPS systems have 5-inch screens that are easier to read at a glance. Bigger 6- and 7-inch screens are available, but experts say these can block a sizable chunk of the windshield; they're best suited to very large vehicles like full-size pickups.
Voice commands can make navigation safer. This is one frill that's really helpful. Upper-tier car GPS systems work by voice commands, so you won't have to take your hands off the wheel.
What maps do you need? Basic car GPS systems come with preloaded maps of the United States. Step-up models add maps of Canada, and they usually don't cost much more -- but the model numbers are always similar, so double-check that you're getting the right maps.
Are map updates included? It's smart to buy a car GPS system that includes free map updates for the life of the unit, experts say. It'll add maybe $20 to the price -- but a map update costs $60 to $80 otherwise.
Do you need traffic alerts? Free traffic alerts usually cost just a little extra on budget navigators (high-end units automatically include them). These work well in tests, steering users clear of traffic jams -- but only on major highways. On city streets (even in major cities like New York) and side roads, GPS systems usually have little traffic information. If you don't drive in well-covered areas -- or you rely on a smartphone app like Waze or Google Maps for your traffic info, which some owners say works better, you may be able to skip this feature.
Could you just navigate with your smartphone? Free smartphone apps like Google Maps can do nearly everything a standalone car GPS system can do -- and did we mention they're free? However, dedicated auto GPS units can be easier to use, easier to see, and they won't drain your phone's battery or eat up your data plan. See the discussion in Car GPS Reviews for more car GPS vs. smartphone pros and cons.