Nibali and Landa are not that clear a favourite on recent form in my opinion. Landa is still a dodgy TTer and Nibali has shown little or known form.
It seems to me that Nibali is having a quiet spring even by his usual standards. I've looked back at his stats for 2013 and it seems that he is riding a fairly similar race program, although the big difference is that he won both Trentino and Tirreno-Adriatico that year.
The amount of TTing in this year's race does give him a massive advantage over Landa though. And Uran, for that matter.
It could be a very open race.