For what purpose you play your PC?
Daily routine or extreme gamer?
For daily routine and not too big screen [max 1280x1024], with tight budget, I would recommend 7600GT.
8800GTS 320Mb for extreme gamer.
Yeah, I would recommend NVidia better than ATI because of the quality of the screen/picture, if you are a "real" gamer. If the quality does not bother you then choose ATI.
Just look at this link for comparison.Quality picture of NVidia VS ATI
It is written in Indonesian Language but you can look at the picture quality differences.