Beast:
Beast has been on board since day one, and has been the soul and moral compass of the team all along. His brilliance is only matched by his compassion and reason. He also has to deal with a far less human appearance than most other X-Men (at least the main ones). Like Data on Star Trek, despite the fact he seems inhuman, he actually represents the best in people. If I have a favorite X-person, it's going to be Beast.