From a study in which college students were subjects in a computer dating experiment, the primary determinant of how much subjects initially liked their date was

I believe the correct answer is the date's physical attractiveness.

When it comes to initial contact with someone, usually the first thing people are going to notice is physical appearance. If the person is attractive, chances are that people are going to like them initially. Whether or not they continue to like them further along the path depends on their personality as well.