For me the Lexus SC430 is the fastest (I have the Petronas one) compared to the Yellowhat Supra and the Epson NSX. (GTR is on my list after I went to the max Cr. of 20mil currently at 15)
It is also the "easiest to drive, all three are in about the same Lap-Time-level though.
Supercar-seasonal Eifel:
Lexus 1:02.9xx (average of 1:03.1xx)
NSX 1:03.1xx (average of 1:03.3xx
Supra 1:03.3xx (average of 1:03.5xx)
The Supra is a bit down on hp but also a smooth ride. The NSX is a bit tricky due to its Layout (MR instead of FR).
I think all of them are good Cars and it doesn´t matter which one you buy (go for the looks).
EDIT: Forgot about the Nomad Diablo, it is the fastest with a long Distance (haven´t used it though), but tricky.