Now some (I'm sure you can guess who) will argue the validity of that statement, because it was made by a Thanosi (even though Thanosi share the same thoughts/ambitions as the real Thanos.) I pay 'those people rabid fanboys' no mind.
Jurgens Mangog...he was still beastly to the point where it took internal damage from the Anti-Force, at the time one of Thor's most potent attacks, to put him down. It's closer, imo, but I don't see Onslaught winning unless he's full potential or whatever.
I think Mangog was created as a "God-Killer" character. Maybe, one of the first in comic books.
He was made to be the ultimate physical villain.
As much as we have talked about his abilities, in the forums, nobody has really paid much attention to the potentially unlimited power-sources he has been able to tap into.
From a more recent standpoint it took Thor alone to out down mangog.
Whereas with onslaught it took Thor plus virtually the entire marvel earth to put down onslaught and crack that armor...
Onslaught also has attackeD people psionically... Removing the even cytorrak gem out of the unstoppable juggernaught albeit off panel...
__________________ 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."
It took Classic Odin death to defeat SA Mangog, that alone says more about how powerful SA Mangog was, even Classics admitted he couldn't beat SA Mangog, and Classic Odin with feats is up their cosmic hierarchy!