i had an old and glory ati rage 128 pro and after my geforce 350 GT an ati radeon 9800 pro, afterwards an geforce 6800 (now) so i can defintly say NVIDIA > AMD & ATI!!11111
Nvidia are by far and a way better for all forms of driver implementation and different platforms. They're more stable and don't crash your pc if you don't install the driver properly. My laptop had a geforce 6200 and my main PC at the moment has a ATI x1950PRO, just to show I've no bias :P (Also bought a geforce 6800GT but never used it :'[)
ATI© is awesome. They have a long history of making the best 3d accelerated video cards [1] avaible.ATI© cards are innovative, powerful and engineered with advanced stability, graphics solutions by ATI support creativity and productivity in business, education, entertainment and production. Visit http://www.amd.com/us-en/ for more info and to find your local retailer for Ati© 3d Accelerated video and performance© cards.
nVidia = better for gaming