Offense - Peyton Manning. Only modern era QB that calls his own plays. Just carries that offense year to year, even when the Colts defense lets them down. Too good.
Defense - I would probably go with Bob Sanders. The guy can just plain play and he's a leader.
Hate to pick two Colts players, as I'm not a Colts fan, but it is what it is. Guys like Mario Williams, Patrick Willis, Adrian Peterson, etc. can play. I just don't see them as leaders at this point. It's not to say they won't be either, so no need to go there.