By watching the way he treats his coaches and players, perhaps?
All I can say is that if I were a parent of a prospective football scholarship player, I would want the influence of Les Miles on my child over the influence of Satan - er, Saban - every day of the year. From an outsiders' perspective, the impression that somes across to me is that Miles treats his players (and his coaches) as human beings while Nick treats them like inanimate playing pieces to be used and thrown away once they're worn out.