either though evga usually costs less. fx has a tranferrable warranty and they have really gotten better from the infamopus 6xxx series crap cards(including the "why the hell are there capacitors missing on the back of my 6800gt" special edition) and crapy support which was about as fun to do as getting run over by a tank for about an hour and a half. Now there are quite a few posts praising the xfx tech support and quality has seemed to pick up too.
evga on the other hand has been top notch for many generations of nvidia gfx cards.
as of currently, get whatever is cheapest.