I don't even know if there is a fundamental difference in what brand creates the 5970. some people say saphire is the best while others say xfx is best. Either which way i have to choose between a saphire or a asus 5970 card. But i don't know how to differentiate between the two because up until now i only used them not selected which one.
Currently just about all of them are made exactly the same with the same PCB design and cooling. I believe that only the Sapphire Vapor-X model has after market cooling and it also has slightly raised clock speeds. Other than that, the only difference between them is the bundle and warranty. Well I suppose there is the box art too ^_^.