even though i prefer nvidia, i'm going to go ahead and say the r7 260x even thought the GTX 750 Ti is slightly faster on average (5%) why? because you can get a second one and crossfire them in the future if you choose to. the GTX 750 ti can not do SLI so you will be forced to buy a whole new set up. if you are completely against SLI or CF, then go with the GTX 750 ti
also, you should go for the MSI R7 260x. the Asus version has horrible reviews because of the faulty fan design.