I would personally reccomend to you a Stadium Truck. You can run the truck onroad or offroad, having a blast wherever you run it. Jump ramps, slide around in the dirt/grass etc etc and they're a blast!
With the onroad cars, your asphalt bound, period. Once you hit the grass your running to save your car! I wouldn't get a car unless you have friends that have them and you can race around with them, or you think you'd like to race onroad cars at a track. Otherwise, I'd stick with a truck.
Also check out 1/8 scale buggies or maybe even monster trucks, they may interest you more than the stadium trucks do, and you'd have just as much fun with them.