Depends what they all have left, I think Dirrell's inactivity will cost him against either if the fight was tomorrow. But pretending he was active the questions are how much you rate Froch's performance against Bute, whether or not you buy into the theory just to his style he will continue to improve due to his best attributes not being dependant on youthfulness and how much you think Kessler is out of his prime imo.
I agree Dirrell definitely deserves a shot at a unified champ because he was able to beat 1 Journeyman in the last year and a half.