It's hard for me to rank them especially since Ingram is still playing. Bobby Humphrey is without question one of the top three RB's to play at Alabama IMO. Right now I would probably rank them Humphrey, Alexander and Ingram with a star by Ingram's name because we don't know his final career stats. If Ingram has another year with 1,500 yards rushing I would probably rank him number one.
Johnny Davis has been mentioned. I think it's great that he is being mentioned, but I would classify him as strictly a FB. He was an outstanding FB and I would rank him as the best FB to ever play at Alabama.
Back to the RB's, I can't argue with Musso and Wilbur Jackson on this list. These were to great RB's IMO.