hi i think if you prefer red or green is your biggest choice the 760 is infront but not by heaps. personally i would go a 760 but im nvidia fan. if you can put the $55 into something else to boost your system then you maybe at better value to got with the 270x. check out the comparison on the link above for details of the 2 cards. note they are reference cards so if both cards are oc'ed then they will perform better
If you would utilize the features that are included with nVidia such as ShadowPlay or G-sync then go nVidia. Otherwise, if you just need performance then go with the 270X. A $55 premium isn't worth it.