Indeed. The M3 GTR, and every other BMW in recent years were tested and refined at the 'Ring. Nowadays pretty much any at-least-somewhat-sporty car goes through the same thing, anyway...
My favorite car for the 'Ring in GT4 would probably be the E60 M5...
I personally love the BMW M5, other cars don't seem quite right on the Nurburgring but the M5 just flows around the track, that lovely smooth V10 pulling hard and the 7 gears are a real boon on the 'Ring, some cars are left off boost or without power because the ratios don't suit the track but with the 7 speeds it's never a problem.
I kinda like the 99 Aston Martin V8 Vantage stock ... or even better with a wing for downforce ... just fun to be in a car that big and heavy but seems to handle like a car almost half its weight
the Isuzu Bellet GT with just an oil change and the body refresh. Not that powerful but just the right amount of rear grip. ie not much.
After finishing all the races Ive been going through a lot of old cars and taking them to the family cup for the ring set of +3. Its been quite fun though I usually pass the next best car not long after Karussell on the first lap.
If you like challenges, then go for the Auto Union on R1:s an dtake away as much downforce as possible. THAT is fun! Other than that, I´d go with the rest and say M3 GTR.
Hmmmm..that's a toughy, but for now I'd have to say the Toyota Minolta Toyota 88C-V Race Car ..yeah, that mf'r can scoot.. although, a close 2nd would have to be for the BMW M3 GTR.. another cornering monster... now if I just had one for real get'n to work wouldn't be such a pain.. LoL !!
original AE86 Trueno, fully modded.. performance and driveability in smooth balance. on the other hand, any car with decent power/weight ratio is good, as long as it can turn and stay on road. 'coughcoughNON-RUFScoughcough*
to 
and back again like nothing else 
