@mugginz: I've documented my complete experience with multiple monitors with both nvidia and ati (search my post history). My conclusion was the ati was both simpler and more flexible than nvidia in multi-monitor setups. Notice how I am talking about multi-monitor setups *specifically*.
Wine tends to work better on nvidia but this depends greatly on the games you play, so YMMV. The few games I play work fine both within and without wine with ati.
There are a few well-known issues with ati: lack of vsync (recently fixed), lack of video acceleration (works for some), slower updates to new kernel/x versions (apparently fixed in 11.1). OpenGL support used to be measurably worse on ati but the gap has all but disappeared now: both ati and nvidia have bugs in their OpenGL drivers and both take their sweet time fixing them. It's just a matter of what bugs you hit.