Im going with the C5R.
In terms of its only close competitor, the viper, its handeling is far above the vipers par. In a real life scenario, or in game the key element is power to the ground without subsiding necessary cornering ability to do so. In nature, the viper is nothing more then a drag race car, whereas upon conception the basic chassis design and weigh distribution of the vette is that of an AutoCross car.
Pulse, I don't know what your so happy about, the AI is terrible in GT3. If it were me driving any of those 'heavy rear wheel drive muscle cars' stock, I would have left you sitting.
Also, I garuntee you in modding that spinly little Japanese car you spent twice as much money as the Z06 Vette costs stock. And Five times more then the Camaro, which given a little tuning is the best american car to buy straight from the dealership.
The cab-forward design projected by Chevrolet, or GM in general is the reason the cars preform so well. Which allows for quicker weight change during corners, and better response time since the weight focus's on the nose but the traction stays in the rear. I don't know how many of you do actual racing in real life, but when it comes to chassis set up, the more weight transfer you have in the corner and the more you can focus it (I.E Cab-Forward) the better your lap times are.
Thats more then likely the reason that Team C5R does very well IRL.
-Sominon.