If you want the best bang for your buck, a super car you can drive everyday and not feel pressure, something that is reliable, more affordable to maintain than any other super car, will attract a LOT of attention because it's still new, yet not seem so outragious, a car you can mash your brains around in a corner, or go for a nice easy long "grand-tourer" drive, spend less money, and use the rest for whatever upgrades you want, go with the GTR!
There is no better car on the market right now that gives you most of everything you want in one package!
That said, the rest of the cars you listed, the Audi, the Porsche, the Ferrari, all do some things very well, and others not so! However, what happens is that they become "sunday" only cars because of all their quirks (exception maybe the Audi), because they become either too loud to drive all the time, too much in terms of unpractical and "common" (the Porsche), and not fun to maintain (the F430 and it's clutch issues).
So Get the GTR, keep the rest of the cash in your wallet for upgrades when you see fit, drive it everyday (in any weather condition) and still have the performance to destroy all the other mentioned cars around a track without breaking sweat!
Cheers and good luck!