Bourque. He consistently showed that he was the best leader in many years. He never won a Cup in Boston, but being a leader has nothing to do with the championships, but it has to do with how you work with your teammates, and how you inspire them. A leader can't be the one responsible for not winning a Cup, that's up to the whole team. That's what happened in Boston, but Bourque was the leader for so many years, and he was respected by everyone in the league.
He never let his anger take control of him, he never bad mouthed other players, but he showed everyone on the Bruins that someone in every group is a true leader, and Bourque was the true leader of the Bruins for 20 years.