The gtx 570 without doubt however.
If you can manage go for a 6970 as they really are not much more then the gtx570 and out perform the gtx 570's in most sectors. Especially if you choose to play at 1080p as the 2gb vram on most 6970's will help you out. I recently ordered the HD 6970 iceQ Turbo 2gb after reading up reviews vs the gtx 570. However i think either card would be great it just depends on what you need.