Obviously Murray still has more to prove if he wants to be compared to the other 3, so I'll ignore him here. It's usually Federer that people say is worse but I think they're all pretty much the same mentally. We've seen: Nadal give up a final set break in AO final. Nadal get dominated by Djokovic. Nadal lose to Rosol. Djokovic putting in a meek performance for most of the FO final. Djokovic's hit and hope strategy utterly failing in the 4th set of the Wimbledon semi. Djokovic dominated in the olympics semi and Cincinnati final. Can we all just agree that what we see as mental strength is just 99 % how they happen to be playing at the time? If you took that first Nadal example and it was Federer giving up a break to Nadal, this site would have exploded and never forgave him.