Defensive midfielder
He is a great passer of the ball, with even greater ball retention, meaning he doesn't lose the ball very often, even if that means passing is sideways or backwards. He also have the best positional play I have seen since Gilberto Silva. Remember he is playing alongside Scholes, who doesn't even jog any more, in a 4-4-2, and he keeps the midfield solid basically on his own. No other midfielder in the Premier League does that as well as Carrick.
Maybe Arteta or Barry had a better season (very similar players) but I think that because Carrick basically controls the midfield on his own for large parts of the game, he get's the nod for me.