Note that the question is not which car you like best or whoch car you can or can't drive, rather than which car you consider to be the fastest overall.
No mention of the '07 Impreza I'm doing 7'01 races from start to finish in it...must admit though good NSX and F430 drivers are VERY hard to get past!
The R8 is great around corners, but it has no ability to overtake on straights unless the other racer makes a mistake. If it had enough power, it would definitely get my vote. But since it doesn't, I voted for the F430. Blows away almost everything else on the straightaways.