I use an ATI Radeon 9700. I've never been loyal to any company, I'd stick to whatever works best at the moment. I love my ATI, it runs maya very well, it runs games even better. As for drivers, they are pretty good, far better than they used to be.

For high-end work with overlay planes I'd go for a Quadro FX. The high-end cards provides alot of memory usually and some hardware acceleration features that aren't available for consumer cards. Also their drivers are optimized towards 3d programs rather than games.

There was a thread here recently linking to a large comparison, check it out. Also, unless you do a large amount of hardware rendering (unlikely, if you do, you'd know), it's in the viewports you will notice the increased speed. The main maya renderer and mental ray is completely independent of graphics hardware.