Right now, Luffy.
BB's been chilling for 2 years on that Yonko title, attacking DF users when need to, and for the rest partying in his hive base.
Luffy shocked the world at Marineford, both with his actions and with his lineage. Then he disappeared. For two years people speculated about his whereabouts and fate. While BB consolidated power, Luffy reappeared out of the blue as a complete unknown entity, started causing havock on both sides of the Red Line, dethroned a Yonko in under two months, then proceeded to murder the Genius of the Future, who in turn confessed to the entire world an incoming apocalypse.
BB may be some monstruous figure who does as he pleases in some remote part of the world, but Luffy is a catalyst for chaos and destruction, popping up here and there unexpectedly.
As an average OP normie, you can live your life on your tiny insignificant island confident that BB will never have anything to do with you, but Luffy? That mofo could materialize at your port at any time!