I would recommend a Full-sized pickup. You can only fit one two passengers in it. They use alot of fuel, so the kid will be driving only when absolutely necessary (cuts down on joyriding). And they are big and heavy enough to smite other vehicles in a collision. Plus you have easy access to a truck for your own needs.
Pickup trucks have a tendance to fold in half at the cab/bed interface in a serious accident. That would be different if they cab and bed are the same part, as is the case with the Honda Ridgeline or Chevrolet Avalanche.
A little food for thought before letting your teen behind the wheel from Autoweek http://www.autoweek.com/apps/pbcs.dll/article?AID=/20080910/FREE/809049969/1506/WEBLOG
An old NY City (like) taxi cab.
Safe - lots of mass and will wipe out anything (short of a semi) it it’s path.
Economical - The insurance should be dirt cheap.
Best Gas Mileage - It is a proven fact that all vehicles get the same mileage when not driven. Given that they won’t want to be seen in this, they will get lots of rides, which will save a lot of gas.
