I've been driving and loving the BMWs in the GT3 class (though M3 was never GT3 was it?) and the R8. The RUF is impossible for me to get right, even with the best front downforce set up she still understeers or will oversteer in response. The McLaren was a favourite but I find if I get the power down coming out of a turn I get uncontrollable oversteer. The 12C GT3 was apparently a headache to race IRL so yeah... no surprises.
Similarly the SLS AMG was a nightmare to set up IRL because of the limited aero profile changes, so I've not really bothered with that. I think the BMWs are the best I've seen, and I'll race them or the R8.