GTX 660 Ti or Radeon 7870 (the additional feature)

Hello,
I knew, this topic asked too often. I saw a lot benchmark, lot comparison site, lot review, and they trade blows in one game and another. I knew very much of these card, even i dont have them now,   .

What make me very confuse is, with a little change of game setting (like AA), it'll make the performance table change beetwen them. Argh, why so confusing just to buy graphic card   . In my country 7870 price between $240-$260 and GTX 660ti $270-$300. I use i5-3470 OC to 3.6GHz and asrock z77 pro3 if thats helping.

So, the question is, did out there someone ever use both of this card and tell me the difference of these card? What the weakness of one card to other, what type of game setting make one card better, etc.. User of one of them can give me advice too of course  . And then, if i use SLI or Xfire, which one will perform better? Because i think i'll add another card later (maybe one-half year later  ). And please, dont refer me to more expensive card, i'm student with a very tight budget   (now you know, $20 difference is very much to me)

This really make me confuse to choose, because benchmarking website show 660 ti perform better than 7870, but other site show 7870 perform well too (even beats GTX 660 TI for some games) for that price range..

Thank you very much for helping me choose