Gonna have to go with Amu. Rika really isn't my type, and she's got that dual personality thing going on. Plus, she's used to dying in painful ways, so she probably wouldn't mind taking one for the team. Ahiru is a duck. A moe duck, perhaps, but a duck nonetheless. I eat duck all the time. Ducks die rather often, so I wouldn't feel all that bad really. Sakura is a bit too juvenile in demeanor. It's be hard on me, but shit happens.
On the other hand, hearing Amu curse my name while dying horribly would break my cold black heart.