The best body type for on road self-driving purposes is the standard race body type.
Probably the first thing that comes to mind when thinking of an RC car, a standard race car.
This body type is the fastest and the best on paved, flat surfaces and is meant for on road use only.
Buggies are the golden middle between an off-road and on road RC car. That being said, they can go off-road, unlike a regular racing car, so that makes them the best bet for people that aren't sure if they want to go off-road or on road.
They are the second best thing on the road but the slowest off-road.
Truggies are also an in-between body type, but they lean more to the off-road role, as opposed to the buggies. Consider them a buggy with monster truck tires.
They're the second fastest body type off-road, and the third fastest on road.
These are your regular monster trucks. For a self-driving application, they'd be pretty bad, since they tend to flip over while making on road turns, so it's best to stick with them only if you're planning to go off road in the woods, grass or dirt.
They are the best for going off-road but the slowest for going on road.