#2 Kenny Omega
While the rumors are wild that the Cleaner has signed with All Elite Wrestling, nothing is official yet, and so Kenny Omega can still be a part of WWE. If WWE manages to sign Kenny Omega, the best stage they can choose for his in-ring debut is the Royal Rumble match.
If the WWE decides to book him as a face, then they could have R-Truth move out of Chase Field just moments before his entry, as a friend would call him up for dinner or any other comedic reason, and then Kenny Omega's music could hit, and the Cleaner would make his grand entry.
But if he is to be booked as a heel, then the creative team can straight away have him attack R-Truth backstage, and then Kenny can enter the match at #30.
Either way, this would definitely be the best stage for Kenny Omega's debut.