McGregor vs. Diaz 3.
It's hilariously obvious but that's the biggest fight to make, with all the hoopla and the instant name recognition you won't even have to do promos for it. For an event as supposedly "big" and "crazy" as UFC 300, it's the most amount of spectacle one can get given the short amount of time.
It's also as inconsequential a fight one can think of (in terms of actual merit or legitimacy to make a dent in any decent rankings) and it'd be hella fun watching those two knuckleheads cave their heads in again with their knuckles.
Whatever the fuck happened to it?