They seem to be very similar first, but all of them have their own character and a slight advantage over each other.
The Lexus SC430 is probably the best allrounder, with a good acceleration uphill.
The NSX is the most agile thanks to its midengine, but therfore it is unstable at the same time! You are gonna wear down tires alot faster no matter how smooth you are driving.
Supra is slightly less agile than a NSX but more than the rest, you`ll notice you are allowed to apply more downforce which is a good indicator why. Slow acceleration in comparison.
GT-R seems to be the fastest car overall from my experience, probably best acceleration, good and reliable cornering, highest top speed (I am not sure).
IF you tune all cars a GT-R will come out with a noticeable advantage in power for some reason, although they all start with the same horespower!
I have very few experience with a Nismo Z but it should be similar to a GT-R but with more torque.