Of course, Nvidia sells some chips as well, but they're usually far too stock, so you'll certainly want to pick one of the firms you named. As for which firm to pick, I'd suggest XFX as I have had only good experience with them and they do provide good chips. But best thing is to dig into the tech side of everything and compare all the specs - core MHz, Memory MHz, memory type, memory bandwidth and so on ... - then you can see which has the best price/performance ratio.