#1 AJ Styles

AJ Styles appeared on the most recent episode of RAW after a brief hiatus from WWE. He appeared in a backstage segment where he confronted his friends Luke Gallows and Karl Anderson. He reminded them of their glory days in WWE and motivated them to get back into the groove. This segment on RAW hinted at a reunion of The Club after almost 3 years.
The Club was highly successful when the trio initially got together in 2016. The Club annihilated the likes of Roman Reigns and John Cena in 2016 before brand split forced them to part ways.
Now that all three superstars are on the same brand, the prospects for the reformation of Club have increased. RAW currently needs a fresh main event heel challenger for Seth Rollins. Although Drew McIntyre, Bobby Lashley, and Baron Corbin are present, they have already had numerous matches with Rollins since last year, so a heel AJ Styles might be the perfect antagonist for Seth Rollins moving towards SummerSlam 2019.
AJ Styles already lost the Universal Championship match against Rollins at Money in the Bank. In order to get back at Seth, Styles might reunite the Club at the upcoming PPV and attack Rollins after the Universal Championship match.
Everyone will be expecting an attack from Brock Lesnar during the PPV, so an attack by the Club on Seth Rollins will definitely shock the WWE Universe in a refreshing way. It might set up a blockbuster Universal Championship rematch in the near future. Also, it will signal the end of Baron Corbin's interminable feud with Seth Rollins.