Originally Posted by Celeras
nVidia is best for 3D.
AMD is generally better for multi-monitor.
nVidia does multi-monitor 3D.
AMD has the capacity to do more displays with less hardware.
nVidia has better drivers and developer support.
AMD is typically priced lower, though they took a weird strategy with the 7970 this time around.
I think that's a fair summary.
Drivers is not as cut and dry as that. Everyone has different experiences with both.
I've noticed in my years (and even more recently) nVidia tends to throw weird errors and has physics issues. ATI has problems with hard crashes and incomplete support. I wouldn't give one an edge over the other, BOTH have glaring issues, neither are close to perfect.
ATI has had in the past, consistently better image quality in games. Awhile back it was shown that nVidia directly subs out IQ for performance. Unsure if that is still true.
With stock revision cooling, nvidia tends to be quieter and run cooler. ATI tends to run hotter (still within limits). With board-partner revisions, this really isn't an issue.