I've had serious trouble in the past with both NVIDIA and ATi Drivers. Currently both companies have equally good drivers overall from what I have seen and used.

The 6800Ultra and the X800pro are pritty evenly matched in most non SM 3.0 games. If SM 3.0 ever catches on the 6800U should match an X800XT. If I had to chose between the two I would go ATi, manily because of its smaller physical size and the fact that it only needs one molex.