Those two cards aren't even close. The 660 ti is more than twice as fast as a 7770. The GTX 650, which uses the GK 107 mobile GPU, is a bit slower but is a much better comparison to the 7770. The GTX 650 ti, which uses the desktop GK 106, is a bit faster but also a better comparison than the 660 ti.
On the flip side, a better AMD comparison to the 660 ti is the 7870 or 7850. The 660 ti falls right in between the two and is very close to both.
If you had a choice between the 7770 and the 660 ti, you should definitely go for the 660 ti. There are some mobile GPUs that perform better than a 7770. It is more of an entry level card for people who want to play games in directx 11 but not on high or even medium settings. A 660 ti will...