Even though they say the ATI is a faster card, Nvidia wil always be my #1 choice.
NVIDIA GTX 590 vs AMD RADEON 6990 Round 1: Length, Size & Measurements
NVIDIA GTX 590 vs AMD RADEON 6990 Round 2: Heat, Noise & Power Consumption
NVIDIA GTX 590 vs AMD RADEON 6990 Round 3: Performance Review & Conclusion
Ding Ding Ding!!
6990:+ runs a little cooler
+ a little cheaper
- much louder
- marginally inferior performance in some tests /
+ marginally superior performance in some tests
590: +marginally superior perforfmance in some tests
- marginally inferior performance in some tests
- a litle more expensive
- runs a little hotter
Ultimately the cards really are very hard to differentiate according to performance and specs.
The only factor really being pushed is the noise level of the 6990.
Also bare drivers and compatibility in mind when buying one.