I too am biased and only choose to use ATI. I currently have a fairly dated x800xl and am more than pleased with it. We use SLI stations at work that piggyback dual gForce cards and they are horrible. Even top of the line cards, but they are worse off than a single high end ATI card through SLI. I seem to think it's driver related, but then again, what do I know.
My advice: Go as high end ATI as your wallet will allow you. If even more money allows, go SLI and piggyback dual ATI's. DREAMY! (AGP is on it's way out.... SLI is making sure of that. Go PCI)
Gary Noonan
'01 S/C VX / '18 Forester XT