#1 AJ Styles - Won
It may seem odd that the WWE Champion required a win at the PPV before WrestleMania, but Styles is a 2-time WWE Champion, and has won high level matches against John Cena, Randy Orton, Roman Reigns and Kevin Owens. This CV in his short career in WWE means he has the support of the office, but hasn't had the chance to show it on the grandest stage.
At this point in his career, the 'phenomenal one' needs a WrestleMania match against Shinsuke Nakamura to cement his spot as one of "the guys" in WWE. With Nakamura likely to win at 'the show of shows' and a possible move to Monday Night Raw for The Phenomenol One, Styles will need to have as much momentum as possible before making that jump to go head to head with the likes of Reigns, Rollins and Braun Strowman over on Raw.