I'll go with galactus. What he did to the entire annihilation armada with a single blast leads me to believe there isn't much a full powered galactus would fear from the green lanterns
__________________ 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."
Rank and file lanterns are basically cannon fodder anyway, so to Galactus they won't be any trouble, an omni directional blast could take out many of them.
Or a wide blast like what he did at the end of Godhunter, where after consuming only one planet he reduced a fleet that used to belong to a very powerful alien empire to a bunch of burnt up husks.
__________________ 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."
Considering that the Guardians have like -the absolute worst- durability I've ever seen. I'd give this to Galactus. Couple of blasts here and there, they'd all fall down.