Would turn Ambrose, as he is a clear heel (or anti-hero face). It wouldn't help him that much though, since he needs to be a wildcard type, and that can't happen with WWE booking style. It has already been said that Ambrose should be a Pillman-esue character, and that is completely accurate.
Turning Reigns mitigates some of his problems as a poor face, but he would still be out of his depth at the main event level. The guy just isn't that good and instead of letting him grow his career the natural way (start low to mid card and then move up) WWE just continues forcing him into a spot that he isn't ready for. Reigns with Corbin's gimmick would probably be best, especially if he could build momentum in the mid card and work his way up.