What is Novak Djokovic's greatest Grand Slam victory?

2018 Wimbledon

His triumphant comeback title after months off with an elbow injury, defeating Kevin Anderson in the final to signal the full return of a champion.

Djokovic's first Grand Slam title, won at age 20 by defeating Jo-Wilfried Tsonga in the final after eliminating both Federer and Roddick.