For me the McLaren MP4-12C is just un-drivable, it steps out too much. I hear the LF-A is a really good car to go with, and if you head on over to the tuning section of this forum, i think there is a thread there on how to tune it nicely.
The SLR is just too bloody heavy.
You can't get any aero upgrades for the LF-A though, so if you were hoping to do that, maybe look elsewhere.