I think most of the cards are actually just made by ATi themselves, the brand only affects which games and stuff come with it.
Sapphire and Hercules are the only two I know of that sometimes make their own boards, but they seem overpriced to me.
So, as for brand, I'd probably just get whatever's cheapest.
Everyone loooves newegg but I'm sure you could find cheaper prices if you were willing to look around a bit. Newegg seems to have good service though.