1. Old Amy Or Young Amy
The Doctor knew there was no saving both Amys. He knew it the entire time, from the moment Rory met old Amy. He didn't say anything to anyone. He didn't tell Amy the facts, the realities of the situations, and let her make her own choice. He didn't tell Rory what was coming for them both, the fact that they would leave one Amy to die. Not only that, he didn't know which Amy was going to walk through that door. He had no way of knowing who it would be, but he knew whichever one it wasn't he was going to leave to die. He was going to abandon Amy Pond, the girl who waited because he didn't come back for her, again. That's a choice that isn't even human. It's a choice that only a monster could make. Rory didn't want to make those kinds of choices - to become like the Doctor - and honestly, who could blame him?