Here's my honest rundown:
JLB: Surely big enough and strong enough to handle his own and not afraid to
get his hands dirty but I think he's too nice to really have enough emotional investment in a fight against friends to be the alpha. I think MP is the only person he could get forced into being willing to give his all against.
JM: I think his strong devotion to his beliefs would make it take quite a bit to arouse his anger to a point where he'd be willing to throw despite the fact that he's easily the most in-shape dude in the lot.
JR: Too happy-go-lucky to be interested in fighting and by the time push comes to shove the opposition may have already gotten into too advantageous of a spot for him to overcome.
MM: At his small size, he'd either have to be exceptionally trained in fighting or hot-tempered enough to make up for it so the fact that he's super cool and super nice makes him a difficult person to bet on.
MP: Surely ain't lacking in the "will to fight" area but is a bit smaller than JLB and JP.
JP: Very nice dude but I think he could separate himself from that just enough to be able to say "Fuck it! Some ass is getting kicked today and it sure as shit ain't gonna be mine!"