#1 Roman Reigns
Roman Reigns is arguably the biggest star in WWE working a full-time schedule. The Big Dog is a Grand Slam Champion and a 4-time World Champion, but he achieved his most impressive victory outside the ring, beating leukemia twice and continuing wrestling.
While many wrestling purists and hardcore WWE fans do not consider his work inside the ring as the best, the mainstream attention he garners has ensured that he has remained 'The Guy' of the men's division. He main evented four WrestleManias from 2014 to 2018, even defeating The Undertaker at WrestleMania 33.
Reigns moveset mainly consists of high impact moves like The Spear, Drive-by, Samoan Drop. What is missing is a legitimate submission maneuver. Adding a decent submission move, even if it a variant of the commonly used ones, will help Reigns add some much-needed variety and technicality to his matches.
A new submission move can also open up new directions for his storylines (an 'I Quit' match between two Superstars having submission maneuvers is always fun). It will also offer a good look for his in-ring work. Almost every top guy in WWE's history has had a submission move and I don't see why Reigns should be any different.