If it was 15 years ago, before he turned into a whiny little bitch, I'd say Lars.....but today, Liam would show up drunk, headbutt Lars into submission, flip off the crowd, insult his brother, then go and get drunker while Lars tried to sue him.
I think Lars would win. Noel is the feistier of the Gallagher brothers and Liam just seems quiet and shy. I don't know if there's any fight in him. Also, it would seem that Lars would have more hand-eye coordination, as he's a drummer and Liam only sings. : )
Wow tough one but I would have to say Lars because he seems like he holds in all his rage and looses it like a mad man occasionally where as Liam is always p*ssed off and would probably be too drunk to fight