If you're not heavily OCing the HD7850 2GB, the GTX 660 will perform better. I wouldn't pay more than $170 for either of them though.
Your other slightly cheaper option is the GTX 650 Ti Boost
(note the Boost not normal GTX 650 Ti which has a 128-bit memory bus). If you don't overclock the HD7850 2GB the GTX 650 Ti Boost is on par with it (within a few %). However, I wouldn't pay more than $130 for it.
@ saipan : The GTX 760 is a $260 card... which competes with the HD7870XT (Tahiti)
and HD7950. It replaced the GTX 660 Ti after all.
edit: There's a HD7870 GHz edition over on Newegg for $175. The Never Settle game bundle seems to be gone (only Crysis 3) so it's probably not as good a buy as before when it was $200-210 or so.Edited by AlphaC - 7/2/13 at 10:16am