Compatibility wise, both do good. Performance wise, ATI currently has the fastest card. Youd have to break it down by pricepoint, which leads us to bang for buck. Currently, the 4850 is a steal, outperforming all but 5 or 6 of the best cards for well under 200$. Over 200, the 4870 edges out the G260 in performance and price. Over 300, youre talking monster cards, best of the best. The G280 and the 4870x2. Not sure of the overall dominance, but the 4870x2 was just released today, and looks to be 20-30% faster than the G280, and maybe more, and since it just released, youll be paying price premium for it. The ATI cards all come with DX10.1 , looking ahead to future games, whereas the nVidia counter parts are still stuck using only DX10, which means, long term, many benefits from DX10.1 wont be available with nVidias solution. Not sure how long you keep your cards, but if its longer term, DX10.1 is a no brainer. Recently nVidia has had to adjust its pricing way downwards, to even compete with ATI, and we havnt seen the reductions from ATI yet, which will make it tough for nVidia to copy. Theres individual cards thatre exceptions, certain games play better on certain cards, but heres a basic of where were at