You know, if such situations happen to me with "real" clients, eg. they ask me to combo different parts from different graphics I present them, I know that none of them are good so we usually start from very beginning.
If I were you, I would choose design which best reflects your needs and ideas, regardless what parts you like best. Try to provide constructive, yet general feedback, not focused on certain designs, otherwise you and designer get into troubles. Asking designers to use someone's else ideas or graphics is the worst thing you could do.