gtx 1080 vs amd pro duo

[duoPRO]

hello guys, im new in crack world, so i would like to build my small crackstation. im thinking of single gtx1080 or amd radeon pro duo. Could you advise which to buy,  hash/second is key decision. Yes, you can buy 2 gtx 1080 for 1 pro duo, but i want 1 single card. btw. titanx is not considered, so only single gtx 1080 or one pro duo.
thanks