I suppose it depends what you play. My experience of ATi has been a much rockier road than my experience with nVidia - Knights of the Old Republic being the key example. I presume they've probably sorted this out in the years I've stuck with nVidia but back then their cards just couldn't make KotOR work right...something to do with OpenGL or whatnot (not just a Vista thing - this was before Vista was even released, though I suppose it can't help matters much). Got a nVidia, worked like a dream.

On the other hand, players of old Total War games had better experience with ATi. I believe they fixed their problems whereas nVidia didn't really bother. I'm sure it's somewhere on this forum or on twcenter that I read it...not sure, but this is just one example. There was uproar on the nvidia forums about it too but their tech support gurus subscribe to the Apple iPod school of hardware support - 'They'll eventually shut up and get with the times. It's only an old game/model anyway.'

ATi, on the other hand, fixed the problem when it was brought up, which is why I advise them to anyone who wants to keep playing the old one when they upgrade...personally I've never taken the opportunity so I don't know what I'm missing all I know is they both crash when I try and load them up and it's apparently a problem with my nvidia's graphics card drivers. KotOR playability's more important to me than STW or MTW playability (I've never played them, only been playing since Rome which works dandy) so I just roll with it :P