Definitely Matt Damon. He remains humble and down to earth, he's not out to score girls. When his wife can't make it to a function, he takes his mother with. Yet his fun-loving and has an excellent sense of humour and loves to joke around. He cares for the environment and does his best to use his celebrity status to other people's advantage, not his own (check out his work with onexone and H2O Africa).
He's great.