I haven't driven any of the 'fab slabs' except the GT One used in S8. I've never driven any of the open wheelers at all.
But out of the bunch I do have, I have to say I'm very fond of the Raybrig NSX. I have a little seat time in the Denso Supra which I really really liked, too. However, it was somebody else's car and setup, so I can't say I know the car that thoroughly.
My RX-7 LM is very fast, too, but a little high strung. I may have downforce issues with it, though, that are causing that.
I pretty much like all the race cars I have, except the C5R. The handling is good but the front tire life sucks so badly that the car is nearly useless in competition if tire wear is involved.