I think it's 30% chance that Federer wins, 30% for Nadal, 30% for Djokovic, 5% for Murray, 5% for someone else.
You gotta remember that Federer made it to the Wimbledon final 7 times in a row 2003-2009, winning 6 of them. Seriously, 7 Wimbledon finals in a row. He lost last year in quarter-finals but that's because Tomas Berdych was on fire. He beat Djokovic in the semis as well.
Federer's win-lose record on clay is 76% but on grass it's 87% so this is the surface he has the advantage. And if you remember how well he played in the French Open, making it to the final and havin REALLY good match against the King of Clay....how do you think he's going to perform on his favourite surface?
The only reason why people don't call Federer the King of Grass like they call Nadal the King of Clay is because Federer has won so many Grand Slam titles on other surfaces as well, 9 on hard court, 1 on clay. While Nadal has won most of his Grand Slams on clay. But Federer is pretty much King of Grass in the same way Nadal is the King of clay, both of them have 6 Grand Slam wins on their favourite surfaces.