By Tom Barlow, dealnews contributor Few situations in life breed arguments between otherwise rational people like trying to navigate your car through a strange city. That's the reason that personal navigation devices (PND), better known as GPS units, have been embraced by America's drivers. dealnews regularly spots GPS deals, and now that summer vacation season has arrived, many of you may be considering taking the plunge or replacing an older unit. To help you make your decision about what device is right for you, here is a list of attributes for your consideration. A wide screen makes reading the maps much easier. The Tom Tom XL, for example, has a 4.3" screen, a nice compromise between the too-small screens and the gigantic 7" ones, which can be a pain to handle and might impede your view. Entering your destination and other data should be simple, too; navigating through screen after screen to accomplish this basic function is very annoying. Some units have predictive data entry, such as you find on your cell phone. If you find it maddening on your phone, you won't like it any better on your GPS. Speaking of data entry, some models, like the Garmin Nuvi 3790ts, feature spoken commands, but like many other devices such as cell phones, the ability of the device to understand what you are saying varies widely. You may find it necessary to change your enunciation to accommodate your GPS unit. Clear enunciation cuts both ways, as well; you want a device that speaks with a voice that is clear and distinct. Most come with multiple choices of voices, and many will allow you to download more, some from celebrities. Nothing snaps you out of a driving trance like having Gary Busey screaming at you to turn left! It's also handy to have a device that uses spoken street names, so that, instead of simply saving "Take the next left," the unit might say something like "Take the next left onto Park Place." Some people like having the display running a crawling text version of the spoken directions, and this option is available. Another handy feature to look for is the reality view, in which can see a virtual representation of an upcoming intersection along with arrows to guide you through it. Yet another handy feature is lane suggestion, with the GPS unit keying you to change lanes at the appropriate time to prepare for a merge or exit. Not all GPS units are equally savvy when designing a route for you. Most will allow you to choose between, for example, the fastest and shortest routes. Better units, however, will receive real-time traffic reports wirelessly as you travel, which they can use to route you around traffic snarls. The quality of the GPS unit routing is determined by the geographical information programmed into it. It's useful to have one that can find the nearest hospital, police station, gas station or motel for you. Some will even know the gas prices and be able to guide you to the cheapest petrol. Many GPS devices now come with Bluetooth capability, like this Garmin nuvi 1690, available for $150 from Crutchfield. This will allow you to synch it with your cell phone and use it as a phone, to make and receive calls via its speaker and microphone without taking your hands off the steering wheel. And speaking of phones, many smart phones now have apps that allow the phone to act as a GPS unit, so why even buy a personal navigation device? Phone screen size is one reason, and ease of use is also a factor arguing in favor of the GPS unit. In the future, look for phones and tablet computers like the iPad to gradually supplant the stand-alone PND as they become more sophisticated and familiar. Like cell phones, GPS units now go far beyond their core functionality. Some GPS units, like this Garmin nuvi 1490LMT, will allow you to upload music and use the device as an MP3 player for your Lady Gaga fix. Some will show video, either from uploaded shows or from a SD card, perfect for entertaining the kids with some SpongeBob once you're on the highway and no longer in need of directions. They can also serve as photo viewers, to display those vacation pics taken along the way. Portable GPS units can help you as a pedestrian, too. Many now are programmed to guide you while exploring on foot, even in the backcountry. All this remote usage comes at a cost, though; you'll want a unit with long-lived battery if you're going to use it away from the car. Examples of some GPS units we've found at decent price discounts: Refurbished Tom Tom XL 4.3" GPS Navigator, $43, newegg.com. This unit has a nice, wide touchscreen display and comes with a 90-day warranty. Garmin nuvi 2350LMT, $164, Buydig. This unit comes with free lifetime map updates, an SD card slot, junction view, lane assist, and more. Tom Tom Go 740 Live, $195, pcRUSH.com. This PND features an iPod interface, photo viewer, voice recognition, and can retrieve weather, traffic and fuel reports. Magellan RoadMate 9055, $220, Tiger GPS. An enormous 7" screen for those that love them, audio-visual inputs, Bluetooth, and an exit guide make this a workhorse. Tom Barlow formerly wrote for Aol's WalletPop and DailyFinance, and in addition to his dealnews contributions, he currently writes about lifestyle topics for Forbes.com. You can follow him on twitter @tombarlow. You can also sign up for an e-mail alert for all dealnews features.