I remember bits and pieces of the animated series and Genie was quite vulnerable there. As others have said, he lost a good deal of his power when he was freed. I don't think a freed Jafar would even register on Galactus' radar. An enslaved Jafar could possibly best Galactus though. Enslaved genies seem to have limitless power but their imprisonment/servitude + those few rules (no killing, forcing people to love, resurrection) keep them in check.
I'm going to go with Jean. That stroke thing was jacked up (she can shrug off the sun's insane electromagnetism but can't take Erik's? ). Anywho, fool her once. Plus, she's been chillin' in the WHR for awhile and no doubt has some new tricks up her sleeve (like popping his helmet/head like a zit).
@CitizenBane: No, Death said if they tried to bind him again he'd kill them. Asking for his help isn't off the table. And if Death sees Genesis as a threat then...there ya go. According to the wiki, Jesse (w/Genesis) doesn't have any other superhuman attributes other than the Word. He's not invulnerable. I don't see why the Colt wouldn't take him out. Or just a regular gun for that matter. The Winchesters have A TON of tricks up their sleeve. It's hard to see how they wouldn't pull out of this. On a side note..I wonder if Supernatural Death can refuse to reap someone a la Marvel Death. Wonder if he could just give Sam and Dean temporary immortality to win this fight?
Round 1: Winchesters win. They're pros. Round 2: Winchesters w/prep will likely find a way to nullify Genesis. Either kill him outright or remove him from Jesse's body. They also have a wild card in Death. They were warned not to bind him again but desperate times...