Statistically Federer is overwhelmingly favoured to do this. The reason is that his achievement is in the bag and there are no variables to impinge upon it. For the other two guys there's and infinity of little things stacked against them as well as the brute fact of the rest of the field chasing them (albeit slowly - Raonic? Berdych?) as well as Father Time. Of course it could happen or Djokovic could break his thumb in training. Who knows?
It amazes me the amount of people who make pronouncements as though through a crystal ball - "Nadal wil win 5 more majors," "Djokovic will be no. 1 for 200 weeks." Uh huh, what did they say about the Titanic? "Not even God himself could sink this ship.”
“There is no best. There is just the discussion of who is best. Federer, he will always be in the first part of such a discussion.” Rino Tommasi