I did this last year and I'm going back in June to do it again.
I decided on the Audi R8 V10 for my first time. Mainly because I wanted to feel out the program there. The Audi was less expensive to drive, yet it still has the Lamborghini V10. The AWD was really nice on the track too! I've got some track experience on motorcycles, but I'm not great in a car. The AWD Audi was a great car to start with. In June, I'm planning on trying either the GTR (because after I got the Z I'm REALLY curious!) or the 458.