#3 Rusev
After joining the main roster in 2014, Rusev emerged as a monstrous heel who had an undefeated streak of 146 days. After his streak ended, he failed to get a solid push and dropped down to being a punching bag and putting other wrestlers over.
His run as a United States Champion was also short-lived, as he lost the title to Roman Reigns only a few months later. The creative team was then unsuccessful in giving him a proper storyline.
His recent "Rusev Day" gimmick is getting a lot of support from the fans, and WWE should see this as a new opportunity for him to be the top superstar that he was destined to be. His in-ring skills are as good as anyone else's, and a World Championship run will be a huge boost for his career.