RPG. I would want to go quick, and I don't know how good those firing squad guys shoot. Is it still "only one guy has a real bullet"?
Edit: Oh, from the article, at least in SC, three shooters, all with live ammo. I could swear I remember reading something about only one guy having the live round, so none of the squad would know for sure if they killed someone. Though if you volunteer for a firing squad, maybe you don't care.