1. Froome
2. Quintana
3. Van Garderen
4. Contador
5. Nibali
It's going to be very close between Froome and Quintana. I'm giving the edge to Froome because I think Sky will do better than Movistar in the TTT and Froome will certainly gain time on Quintana in the short ITT. They are both going to be in top form when the mountains come; and although I think Nairo is ultimately stronger than Froome in the mountains, it's going to be extraordinarily difficult for him to make up the time difference. However, it's conceivable that Movistar will beat Sky in the TTT, in which case, the chances of Quintana winning will be much improved.
I also think Contador's only chance is that both Nairo and Froome have bad luck and/or make mistakes. I placed him in 4th place because after he realizes he doesn't have a chance; he might try conserving energy for the Vuelta.