Novak motivation has gone downhill since achieving the Career Grand Slam, that title at the French Open took him out a huge amount of pressure but it also drop his motivation and immediate goals on the ATP World Tour.
Roger is the greatest tennis player of all time and in his mind he has already accomplished more than what he ever dream about, this Australian Open title is Cloud 9 for him. He will try to peak for Wimbledon and the US Open, aside from that Federer is just enjoying playing tennis these years.
Andy?, the current World Number 1. Consistency is the key and Andy was really good last year at that, however i seriously think he will not managed to recover that form throughout the year.
Nadal is another case, after winning Monte Carlo and Barcelona last year he seem to recover his great form, then a random injury appear and he miss almost all season. Nadal confidence and motivation right now is higher than any other top player currently in the tour.
I really believe Nadal will have an amazing season, that "Fluke" final at the AO will prove to be no mistake and he might very well finish #1 on the ATP World Tour Race 2017.