My exp. with ATI has been the same - they are a headache. Although their new cards are rated to be faster - this has little bearing on emulation. Anything from a tnt2 up seems to run perfectly (except ATI/voodoo cards.. which mess up textures, crash, and don't work well in XP).
Yes, the ATI card may have more features but if ATI acts like it normally does, it will stop releasing drivers for this card as soon as its next one comes out. Nvidia supports all of its cards. And a passable Nvidia card can be bought for much less than a "passable" ATI card.
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j64: