What am I picking her for?
If it's to be with or get with one of them than Sally, no question. She's more mature, shapely, and I have a better chance with her. Not good chances, what with her being a princess and me being a human, but at least she's not obsessed with one guy.
If I'm picking the better character it's Amy. I like her design (since Adventure) more, and she has characterization that's more entertaining (imo).