You want to make sure that your next car includes Bluetooth and USB connectivity for your phone. This is pretty much standard on most new cars, but if you are buying a used car, you should make sure this is included and that it works.
With Bluetooth connectivity, you can leave your phone in your pocket and listen to music or make calls over the car's system. USB Connectivity allows you to plug your phone in and use a line out feature to listen to music and charge your phone at the same time. Keep in mind that not all car USB ports charge phones fast enough, so you may still need a 12V adapter.
While these connections are very common up front, you want to look for power points that allow a front passenger to charge their phone as well. You also need to look in the backseat and or third row for connection points. The last thing you want is no way for adult passengers or for kids to charge up devices on a long trip.