So over the years Multi-GPU support has improved quite a bit, AMD still isn't up-to snuff at the level of NVIDIA though, multi-GPU supports still literally and directly remains the Achilles heel of ATI's Catalyst drivers. ......
But I would choose neither. With just 9 days till the release of the GTX 560 Ti on January 25th, it's an entirely new question that needs to be asked
Got a 965 be amd overclocked to 4.1 with a 850 certified psu. currently running dual 8800gts that was out of my last rig but i need some better graphics units and have the money now but only 200 enough for 1 right now but in about another month will have another 200 to spend on one. They will running at 8x 8x.
It's just the old Nvidia vs ATI question I think. Depends a lot on what you consider "better" - which games/types of games do you run, and do you have any additional preferences like low noise or low power consumption?