Speaking as a non-Knights supporter, Rochow is the guy that came to mind for the captaincy. I think he's representative of the type of player the joint was built on when they entered the comp and what they need now. No nonsense, tough, big hearted a la Glanville, Butterfield and those guys.
With Rochow's injury issues this year it probably sounds silly to say this now, but I would put a line through Mullen simply because he seems to be on the sideline a little too often. Plus I think a fresher face and someone part of the longer term plans at the club so Rochow would be my pick.