1. Ferrari F12 Berlinetta, easy to pick.
2. Audi R8 5.2, can't remember the year but not the 2013.
3. Corvette Racing GT2
4. Ford GT40 MK II
5. Risi GT2 458
That is a difficult task, and I don't reckon I will try, but that's a good list. Another post mentioned the NSX-R, and I will note that I was very satisfied with mine.
Just took some quick basic shots of them in the garage:
C Class:
At 2,989lbs, and 332hp; it's agile, balanced, and quick. Not the fastest in a straight line, but it makes up for it on the way into and out of corners.
A Class:
(The Heisenberg Mobile)
A bit of a pig, really. It's stable, and it's fun in the corners, but it's strength lies under the hood. 755HP has it at 230mph, with a weight of 3,501lbs.
S Class:
A good all rounder with a bias for speed; it's got a hell of a kick and holds together in the corners surprisingly well for a car weighing 3,494lbs.
Being 2,590lbs with 629HP and the aero package make this one pretty obviously the one that's the all rounder with an edge in the bends. This thing is a monster on a track like Indianpolis GP Circuit.
This one's my personal overall favorite, until I can get my hands on a C7. With 750hp and at 2,657lbs, this one's more specifically tuned. It's my fastest car around Laguna Seca by quite a bit, but on most other tracks I've raced it on it tends to do about average. 750HP and 2,657lbs means there's not really anywhere where it's slow, just where it's not as fast as something else I have.
Which actually reminds me, it would be a fantastic addition to the game if T10 would borrow the garage idea from the PGR games. Being able to walk around a scenic garage with a few of my favorites was so fun.
I can't seem to think of a 5th right now... maybe my DC5 Type-R.
@Minty - I would LOVE to see the garages from PGR make an appearance here. PGR3 was my first 360 game and the detail on the cars when walking through the garages was absolutely mind-blowing!