Lobo - Lobo destroyed his own planet, while he was on it. He'd probably rip off Iron Man's head, get pissed off when blood came out of it, and then attacked a brewery.
The Captain - This is a tough battle. If they use brains, its Hellboy. In an all out Slugfest, The Captain has generic superhero powers including Flight, Super Strength, and Super Endurance. Also, he is too stupid to know when to quit.
Gambit - Tough call again. I go with man who can blow you up by touching you.
Galactus - This isn't even a contest. Galactus steps on New York, killing everyone in New York, including Mysterio and Green Arrow. Case Closed.