well my answer depends heavily on the prize cars that are available once you get all golds in the license tests. That way you get a free car and a good amount of cash to mod it. Or... sell the prize car so you can buy a better than average 1st car....
id take a bmw 325i e30 or any other e30 if it was available, if not a 2002...if i start the game and find this car im goin to jump over my house man! and scream! haha...and then i'd beat the crap out of all those golf gtis and jettas and 1.8is and audis just like i do back home on the autobahn
You really can't answer this question properly without knowing how much money they are going to give you to start out with. But if they are going to have a used car dealership, then I would start out with the Skyline R32 Type-M. The same car I started out with in GT1, and It has always been a good car in all of the GT games