Alabtron has always been fairly good with graphics chips. I havent had much experience with gainward but i'm sure they would both have the same performance. Remember, they both have the same Memory and GPU (VPU).
All the different brands do is make or choose a unique heatsink and put the all the peices together. They rarely add unique features. I'd get the one with the best games or software bundle. That's what it comes down to in the end between these 2 cards.