Buggy will be the first to find the One Piece.

Buggy will find the One Piece before Luffy. One of the longest running gags in One Piece has been Buggy's rapid rise through the pirate world. The logical conclusion would be Buggy becoming Pirate King. However, this is not likely due to Luffy being the one who is destined for that title. However, a funny gag that would be both in character and finish the joke, would be Buggy finding the One Piece first. Given Buggy's traditional views on treasure and that we know the One Piece isn't just gold/money it would make sense for Buggy to discover it and not know what it is or just not think its the One Piece. He will walk away leaving it open for Luffy to discover it. Buggy is clearly outmatched in power by the other members of his crew, it stands to reason that while the fighting is going on he himself would sneak away to claim the One Piece if they Cross Guild/the Straw Hats make it to Laugh Tale around the same time. Right before finding the One Piece seems like the best time narratively for Zoro to defeat Mihawk (who is with Cross Guild atm). At the end of the Laugh Tale section, I could see Buggy getting credit for defeating most of the pirates there and receiving the title of God of Pirates (a name he gave himself in Orange Town).