For me the answer is easy, I choose the ZR1.
The GT-R is a exellent car, but it doesn't feel like a 520hp car. It's quite boring to drive to be honest, it feels like the car is controlling you and not the opposite. The GT-R isn't exactly a looker either, it's not ugly but I think the R33 and R34 looks way better and in the end I would rather take the R33.
The Zr1 is a beast and it's harder to control if you compare with the GTR. But I like it, driving fast shouldn't be too easy cause then I'm getting bored. The ZR1 is never boring, it's exciting, has a proper manual gearbox and looks way better. What's the point of driving fast when can't feel that you are driving fast.
I'm tired of people complaining about the leaf springs, cheap interior etc. If I buy a sports car I want a driving machine, not furniture to my living room. In the end the ZR1 a blast, and that's what matters to me.
But none of them are bad cars, they are only following different philosophies and I'm more of a vette-guy.
Btw, don't forget the sound. I think we got a winner