Currently, if you can figure out how to use linux, Ethereum.
Ethereum can be profitable with a 750Ti, which is a 2014 card, with an up to date card like a GTX 980 it's pure profit.
AMD cards are also supported amazingly by the Ethereum community, an R9 380 is pretty speeding mining. The only problem is the fact that you NEED to use a Linux OS to mine.
actually the big guns works rather on windows, problems occurs when you use smaller cards (or old gen cards) like the 750ti where the whole memory can't be allocated correctly, for these cards, yes linux is preferable.
However, a gtx980 works ok even with windows 8.1 (same applies to my 290x for example)