Nadal and Djokovic have 2, Murray 1. Nadal seems a bit done on the surface judging by his last three awful performances, I think even at his peak he was better on HC than on grass, despite most people thinking otherwise. Grass might be Djokovic's worst surface but his level on it is very underrated, he's been very consistent at Wimbledon since 2007, aside from the time he drew Safin in the 2nd round. In fact he made the semi more times at Wimbledon than at the AO. Many thought that the 2011 run was a fluke and he wouldn't win on grass again, but last year he was impressive. And Murray reached the final in the past 2 years (leaving surgery year aside) and won Olympics, so he will most probably win one more at the very least. I think the next 3 years it will be split between Djokovic & Murray.