Captain's need to demonstrate exemplary behaviour on and off the pitch. You can't have them swearing, elbowing, kicking out and, worst of all, diving. Rooney does all of these things.
Under Fergie, Rooney would never get the arm band, but Moyes might be able to get Rooney to perform under the added pressure. My vote would be for Carrick, or Fabio. I feel the captain needs to be someone whose been around is looked up to as a leader regardless of wether r not they're the captain.