7850 no doubts.570 is about 12% faster than a stock 7850,but you can overclock it to match 580 level performance.otherwise i would go with 480 instead of 570 because-
for $210,it's a steal!
more raw power than a 570.
rock stable drivers
more vram(1280mb 570 and 1536mb on 480).
but once again,i won't suggest any card from 6xxx or 5xx series because 7xxx and 6xx are out.
only fps count is not the main factor,5970 and gtx 295 are still very capable cards but will you buy it? no if you are wise enough.