Since none of them have the slightest chance of assuming office, I care about their policy stances only to the extent that they represent something recognizable to the masses as libertarianism - since the whole purpose of supporting the LP this cycle is to increase the profile of libertarianism. It looks like they're all well within acceptable ideological limits, so the only consideration is who can draw the most votes from independents or disaffected GOPers/Dems.
I'm leaning toward Gary for this reason; he's not going to wow anyone, but he's not going to do anything really stupid either. He's the safe choice.
McAfee's a wildcard: more charisma (at times) but could well go berserk and do something stupid.
Peterson's an unknown, to me anyway, but his Paulish rhetoric is playing fairly well tonight.