Soldat votes Silo, because they think they're more likely to hold off green-eyes than a World Eater.

Stone votes Silo, because he can just fly people to the submarine if the bomb fails. All aboard the dragon express? He will be disappointed at not being able to bite the World Eater, though, but it's probably true that he'd be more effective against potential green-eyes anyway. There's not much that scares him, and he's a lot bigger than they are.