#1 AJ Styles
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Roman Reigns and AJ Styles main-evented back-to-back pay-per-views in May 2016, Payback and Extreme Rules, with Reigns retaining his title on both occasions after The Usos helped counter interference from The Club.
At the time, Styles was still relatively new to the company while Reigns had only just won the WWE Championship a month earlier from Triple H, so it was no surprise that “The Phenomenal One” was unable to bring a swift end to his rival’s title reign.
Fast forward to 2018 and one imagines that a match between the two would result in a different outcome. Styles is now a two-time WWE champion and he is the only full-time roster member whose crowd reactions are consistently as loud as “The Big Dog”.
When you also consider that Styles is undoubtedly the best in-ring performer in modern-day WWE and that a battle between the two would probably be a contender for Match of the Year, then he’s the obvious candidate to defeat Reigns clean one day.