At this present moment - Nibali.
I think its likely Contador at the tour will be better than what Nibali is now, but don't underestimate Nibali now. Times change. I still had in my mind an image of Nibali from 09, 10, 11, 12 who was a top 10 climber and top 15 tter who had a good ttt team and could urk out podiums/ gt wins, when others faltered.
But what he is showing us right now, winning the tt like Contador won the tt in Nvegal - crushing the field, best climber on every stage in quite a decent field (whereas in the **** 2010 vuelta field he wasnt even the best climber), i think one has to realize Nibali has improved.