You might find this interesting.
http://www.tomshardware.com/2007/10/09/directx_10_shootout/
But I'd recommend you to think about what you are going to use it for. If you're more of the type that like good quality, ATI is the right route, however, if you want good performance for high-end games (For instance,
Crysis) then nVIDIA would be the right route.
I've used ATI for a rather long time, and I'm probably staying at this route, atleast for my use.