I've had to uninstall nVidia drivers twice on 2 different computers because they caused each computer to not boot. This is with 2 totally different computers, 2 totally different video cards.
With my main computer, which is ATi, I have absolutely no problem with the drivers and find them easier to install and catalyst is pretty awesome.
I've really never had problems with ATI or Nvidia.
The ATI Radeon 9550 I had so long ago was fine but just low-spec.
The Geforce 6800XT I used to have was fine but died (was old anyway).
The Geforce 8600GT I used to have was fine but low-spec just like the Radeon 9550.
The Geforce 9800GT I have right now is great, but heats up like a whore.
I've never had driver problems with any. I had to update my drivers for my 9550 to get BnW2 to work when it came out though thats it lol.