It's difficult to make suggestions without knowing more of the dynamic in the group. For me the main options are:
Martin - the closest to a Sinfield style captain as a steadying influence; would also know best when to take the two points etc. He'd have to cut out the regular suspensions though.
Sezer - more McGuire style captain, but it might bring out the best in him.
Cam Smith - if Rohan believes that he has leadership potential, maybe, but I'd rather he focuses on improving his game, and cutting out fatigue errors (e.g. forgetting it is the 6th tackle and running blindly for the line). Is he vocal enough?
Handley - I'm not personally a fan of wingers being captain, but he seems to be favoured as a leader in the group.
Myler - an obvious choice at FB and v. experienced. Smith might prefer a longer-term option.
Leeming - fine, but not ideal if he is going to be spelled, and also seems to need to work on his own game a bit more.
Oledski - would be a JP style captain, but again not ideal if he has to be spelled. I'd prefer a gobby half-back type with more potential sway over the referee in tricky situations