#1. To join AEW
The Revival leaving the WWE and joining AEW would virtually guarantee them becoming bigger stars. It is hard to become a top star in WWE when you are a tag team. AEW stars will have no such problem.
The Young Bucks are possibly the most popular personalities on the AEW roster which means any match they have will be important, especially with great teams against whom they can have great matches. The Revival vs. The Young Bucks would undoubtedly be an amazing tag team match worthy of main eventing any AEW show.
They would have so many more chances to be bigger stars with much more focus on tag wrestling in AEW than WWE. This could be the smartest career move for the two and they wouldn't even take that big of a pay cut. If they perform as well as we know they can, WWE will be offering triple the amount they are now to get them back.