Lots of people have said the NSX. I'll have to go with that as well. They're not overly powerful, but just about anybody can drive one no problem. That's usually what I put a new comer to GT3 in after they've said that the slow cars are boring (:
...The best of the best of stock cars....is the very expensive.....Nissan R390 road car. When i first got it(bonus car), i did the Trail Mountain Endurance race. I noticed the great handling at the first corner.. 👍 try it, you'll love it!!
That was after an all night bender at hooters followed by 24 hours of Nascar re-reruns,, they soon after apologized, and retracted their statement saying they are drunken fools.
I think that a couple good ways to gauge this question are:
What car would give you the fastest lap times in a "Normal Car" restricted race?
What "Normal Car" has the best power to weight ratio?
The best car I own for that is the Zonda C12S. Its unmodified Power to weight ratio is 2.192 . The special "S" version of the buyable C12 can only be aquired by winning it.