The 660-based cards will of course be faster than any of the 650-based ones (the 650ti is really just a 660 with one bank disabled, so the 660 ends up being about 40% faster than the 650ti), but thanks to a strange memory setup, the 660ti is only about 8% faster than the 660 in games such as Metro 2033 and Skyrim, so I would go with the "regular" 660 unless you find a sale where they have the 660ti for no more than about $20 extra. The 670 is a cut-down 680, and the 660ti cards are made from the chips that couldn't even qualify to be made into a 670. Not inspiring.
--Patrick