#5 Dean Ambrose

Dean Ambrose is one of WWE's biggest workhorses. He has been working continuously for the past many years without any breaks (excluding the recent injury), but he isn't taken seriously by the masses. He is not getting the push other babyfaces like Roman Reigns or AJ Styles are receiving. His run as The Lunatic Fringe is fun and entertaining, but isn't highly regarded.
Oddly enough, though, he is yet to perform as a heel after the Shield breakup in 2014, so we haven't seen the bad side of the Lunatic Fringe yet. Ambrose is at his best when he's exactly that, a lunatic, but for some strange reason, WWE has developed him into a slapstick comedy guy who will never be the top guy.
WWE should take the chance and turn Ambrose heel. It could be very interesting.