I'd want to know why you'd want a choice of those three only. Any specific park day that you wanted to dine at after? Or were the other two Downtown Disney-specific? I would choose Raglan Road if it were a matter of Downtown Disney being the reason.
I wouldn't choose the luau at all because I have never seen one positive review of it. Usually I like to try a place to decide for myself, but I'm not convinced about this one.