#2 AJ Styles
The phenomenal one is too talented to be kept out of the main event picture. However, as he spent almost all of 2018 as WWE Champion, having him go for it immediately after WrestleMania may not be the best option. Therefore, retiring Batista might be appropriate. One way to book this can be:-
After WrestleMania, Batista gets drafted to Smackdown. He claims, how this is his show and how he is ecstatic about returning home. He also says that he would, therefore, like to wind up his wrestling career on Smackdown.
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AJ Styles comes out and says times have changed and Smackdown is where it is today because he carried it on his shoulders and rebuilt it into a house of opportunity brick by brick while Batista was busy acting in movies. He also claims that he is ready to gladly prove his point by retiring Batista.
This does not go well with Dave who hits back at AJ for not being able to defeat Randy Orton at WrestleMania( In this version, AJ loses to Randy at WrestleMania). He says, he shall agree only if AJ is able to beat Randy at the next pay-per-view.
AJ beats Randy and gets the match. This is patiently built up to Summerslam where AJ and Batista finally clash. After a long and finisher-heavy match, AJ pins Batista to retire him. Batista raises his opponent's hand and AJ reciprocates by showing respect to Dave for his stellar career.