Well. I voted for NSX's since I do believe they are the best all around cars in GT500, with engine in middle they achieve almost perfect balance, they are created for circuit racing. That being said, there are a few from each company that are equally good. Thanks to the amazing community of GT5, I managed to collect them all, I've driven them all multiple times, thus I can say which really stand out.
The premium NSX's are faster than the standard, the standard versions are more agile, more stable and do not burn as much tire. From the standards, the worst being the Castrol and the best (and ultimately fastest) being the Mobil1. The premium versions produce more power and have higher torque levels, thus making them faster, but they cannot be driven as recklessly as the standard versions. They need a really good setup to aviod from burning their tires.
Nissans. Premium ones are really stable and firm cars, they do not burn their tires as easily if driven properly. Their standard versions are not as good, especially the two PENNZOIL versions. Many people are using the premium Xanavi GT-R, I always prefered the Xanavi Z. Same goes for the standard, the Xanavi Z is truly a marvelous car, although it is as fast as the standard Xanavi GT-R, which is my favourite GT500 Nissan model.
From the Toyotas, once again I prefer the standard Supras, specifically the Denso Sard and the au Cerumo. Especially the au Cerumo is my favourite Supra, not only by its looks but its performance is outstanding. Well, it does have a very nice setup, which allows me to battle pretty much all other GT500 cars. I don't really prefer the premium Supras. I just never got into the for some reason.
Lastly, the Lexus cars. Those are the ones I've driven the least. People have beaten me with these, but for some reason when I drive them, even with using setup, I never seem to be able to race as easily as with the other cars.
Overall, I use the Honda's a lot, fromt he Nissans the two versions of Z and the standard Xanavi Nismo GT-R, and au Cerumo Supra. đź‘Ť (feel free to correct me if you think some or all of these points do not agree with your stats).