Ti in graphics cards question?

Hi I have a 2,quick questions about NVIDIA cards and their ti lineup. If I were to get a gtx 650 ti, or a 660, which would be a better buy, I'm looking for the highest price to performance Also, I know a 660 and a 760 are pretty much the same things, so what would be a better choice, the 600 or 700 series? I know the 700s are a little more expencive. Thanks for your help in advance