my hats off to eVGA first, then XFX. i have all eVGA's now, but had XFX and BFG cards (same cards geforce 7800 gt's).
IMO:
evga has the best "stock" overclocked cards with room to oc some more. in addition to lifetime warranty, they have a step-up or trade-up pogram too.
xfx is next with great "stock" overclocked cards that also oc well.
bfg i was surprised to find that they have excellent "stock" oc cards (2) and warranty, but at pretty miniscule overstocking (on the core memory especially) they both had what i call serious artifacting issues. they were fine if left alone.
i have always felt these three were the best to choose from for nvidia cards.