All you probably really need from a system is the ability to get from point a to point b, but once you start using one you'll realize you do have some preferences over your devices features. Before you start your search you can look over some of the available features, figure out what you like, and what to look for when choosing a GPS.
Some of the features available include newer features like touch screens, various kinds of dash hook ups, and smaller sizes. Touch screens make navigating the system easier than ever before. Each device is set up in your car in a different way--some are hooked up to your windshield, some are permanently attached to your dashboard, and others hook onto your dashboard with a suction cup. Deciding how you want it hooked into your vehicle is a big decision that will help narrow down your options when choosing a GPS. These systems come in all different sizes, some screens as small as 3.5 inches.
Navigation abilities are very convenient. With a lot of units you can put in an unspecific destination, such as gas station or hospital, and your system will find the nearest ones for you. This is a great feature because often you don't really know where it is you want to go but know what you're looking for, and your system can save you time getting there.
If you have preferences about how to get where you're going, for instance you want to avoid highways or toll roads, or you want the shortest distance or the shortest traveling time, you can put that preference in and your device will find you a route that works for you. This is a fairly common feature these days and one that should be easy to find.
When you're considering getting a new system think about your own needs and make a list of what you'd like to help yourself decide what to look for when choosing a GPS.