Gainward. Manufacturer warranted overclock (425/1200 or better I believe).
Although I like that eVGA seems to be taking their cards more seriously now, Gainward is perhaps the best nVidia card maker (BFG the only real contender as of now in my opinion). Actually now that I think about it, I'm not sure which one is better. You could step up a few months down the road with eVGA, but Gainward's cards are very nice (I have a GT Golden Sample).
Since you're going with the Ultras, I'd wait as long as possible and then get the eVGA one so that you can step up to whatever nVidia should be rolling out at the end of this year.
Oh, and top-of-the-line cards and bang-for-your-buck don't go hand in hand. You want BFYB, get a Gainward 6800GT Golden Sample. Factory OC to Ultra speeds for about $430 isn't bad.