Three. He's been a mercenary and actually has a ton of guns and experience.
One was a corporation rich kid who probably rarely needed to defend himself. Besides I doubt killing is in One's nature. One would probably just stare him down with a gun and try to talk his way to a peaceful solution.. Three would make sure it got done.
One can kill, actually. He has killed plenty in battle, and he was actually about to kill Three, but some other guy appeared so he had to kill that guy and by then Three had turned so that was opportunity missed.
Yeah but in this hypothetical 1 and 3 would be going head to head right? There isn't an oh I have the opportunity then oh he looks at me never mind. It's a where going through this to the end, and Marcus has more muscle and way more experience. Sure One has killed before but Three did this for a living.
Besides your saying he was going too BUT that was when One thought Three killed his wife, he doesn't think that anymore.