People should look more into the respective games of the players and form, rather than just rankings.
Nadal's draw looks easy because of the combination of players that have similar game, but are of a much much lesser quality, or players that haven't done anything for quite a while.
Djokovic's draw is significantly more difficult, because not only he meets more in form players, but they have strengths different than his own, and can cause a lot of problems, if they catch fire. Still, he gets a much necessary break in the QF, just before the final push, as Nishikori peaked too early for this part of the season (prediction either he doesn't reach the QF, or gets there injured and goes down easily).
Federer’s draw is the hardest, as he cannot (and never will) catch a break from playing players that are just breaking through (similar to his history with Del Po), which means that they are motivated and hungry, on top of being in form.
The two dangerous floaters, and the seriously ramping up pressure by meeting ever more quality opponent in every round makes his draw impossible to get through without arriving in the latter stages/ final in bad condition.
Odds: Djokovic as a favourite, followed by Nadal, and then Federer.
Waiting for a first time winner in Cilic or possibly one of the breakthrough players though.