Sorry, but I think Nefaria takes this. He is way too strong, too fast, too durable. And, he is not prone to messing up in battle.
As a matter of fact, I would imagine that he could take out BB pretty quickly, unless BB gets lucky and tags him with his voice.
If Black Bolt uses his voice Nefaria's as good as dead. Nefaria has no attack that's nearly as fast or as powerful. Nefaria has the edge in pure H2H. However, it might also be possible for Black Bolt to simply draw the ionic energy out of Nefaria.
Iirc a nefaria at his prime is putting down Thor....
But recently wolverine was sent in to deal with him i think...
I'd say black bolt has the better average showings and doesn't have to worry about finding an ionic energy source... Also...
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."