I started with ati for my first kickass video card, the 8500, I didn't have all the driver problems people with it reported, so I have a different perspective, but I like their control panal, and at the time, compared to nvidia, the performance of anistopic filtering, even if it was lower quality, it still made textures nice and sharp.
With my 6600GT, I find the control panal is retarded, and in the type of games I play alot (racing games) compared to R300+ and up boards, ati's fsaa actually makes a pretty big difference at 4x.
I'm def. going back to ati next gen unless ati pulls a nv30, which is unlikely I think.