If you really want to eat in the MK i would say that the castle is more romantic - only due to the setting, but i would try and get a late ish ADR as one CM told me that the younger kids tand to eat earlier - thats not to say there wont be any kids cos there always will be just less very little ones!
If your ok about going to a hotel, citricos is nice, and so is the cali grill and you can watch wishes from there!