The biggest discrepancy between Ambrose and Rollins is in the promo category. The difference could stem from the fact that Ambrose has six more years of experience than Reigns does, but that is definitely Reigns' biggest widely recognized weakness. Ambrose's promos can be almost as unpredictable as his actions are, and they further promote his "Lunatic Fringe" persona. His promos have a lot of similarities to Roddy Piper. His demeanor even has similarities to Stone Cold Steve Austin, especially with his defiance of The Authority as of late. As you can tell from his passionate promo below (from the week after Seth Rollins betrayed The Shield), he doesn't do things the same way as everyone else, and that is what is connecting with the fans more than Roman Reigns at this point.