False Advertising: Thranduil
For my money, Thranduil is the best option—not necessarily to kill Bolg, but to be in that helping-Thorn/parallel fight position. Because seriously, that conflict between Thorin and Thranduil needs a resolution.
Unfortunately, I suspect this never occurred to the PTB because they don’t see Thranduil as a person. More a device. And his purpose in AUJ and DOS was make Thorin look like the most put-upon underdog, who is just treated so unfairly.
But if they’d treated Thranduil like the significant supporting character that he is, developed that conflict between him and Thorin—and all it implied—then keeping Thranduil on Ravenhill (alone or with his army), provides optimal fulfillment/resolution to what came before.
Even without development, though, Thranduil going up to Ravenhill sooner just has more oomph than whatever they think they’re doing with Legolas.