I wasn’t claiming that Maya and Max have better performance, but I have noticed a strong trend that ATI/AMD GPUs tend (at least in the past) to have a lot more viewport bugs or glitches. I know plenty of people that refuse to use ATI/AMD cards because of driver issues and experiences in the past, it’s probably not enough to suggest that you never buy them, but it has created biases.
Here’s 2 random examples of the types of glitches I’ve seen, but I’m sure you could find similar bugs or glitches for Nvidia as well. There’s really no scientific or accurate way to say which one has more issues.
http://www.polycount.com/forum/showthread.php?t=101534
http://www.polycount.com/forum/showthread.php?t=75743