Tim Pawlenty is a serious contender. But I think Obama will be reelected. Pawlenty may be serious enough about it to sit this one out. It's very difficult to defeat a sitting President. If any of the three you mention is the Republican nominee I will be a happy Democrat.
Pawlenty doesn't have a chance. He's not a whack-job like Palin or Newt - but the people in his own state, even his "supporters" feel that he isn't a tough-enough executive.