Depends how much later this year. Right now only 6xxm and AMD 7970m work with no problems, while 7xxm 8xxm do not work at all, the 9xxm require a modded driver and the 980m can only work at 970m speed, however Prema is working on a mod that will make 7xxm, 8xxm and 9xxm work at full potential with standard drivers, so if you are willing to wait long enough you could go with any of the aforementioned cards, though no one knows how long you'd have to wait as there were no news of progress since ~2 months.
Anyways, as it is, if you don't want to get your hands dirty 680m and 7970m are your only options, while 970m offers the best performance out of all cards that work.