Nadal for me. People forget that he shut the 2012 season down after Wimby, and had the major knee/lower leg injury, resulting in surgery. ALL the "experts" SWORE that he was gonna retire, and that THIS injury would be the one that ended his career. Those roars got even louder when he pulled out of the Aussie Open.
Not only did Nadal come back, he had arguably his best season--10 titles, 2 Slams, 5 Masters titles, 3 Masters titles on Hardcourt, becomes only the 3rd male player to since 1990 to win Canada (beating Fed and Djoko back to back), Cincy (beating Fed again in a terrific match), and the US Open triple, etc. When judging these seasons, I think much more has to be taken into account than just analytics