Are People Most Often Attracted to People within their "League"?

I seem to be attracted to people who are about as attractive as I am, but I seem not to be attracted to people who are significantly better looking (Except from a purely aesthetic standpoint) or less good looking than I am. In the real world, most couples I see are more or less equally attractive. Do people most often have crushes and fall in love within their own "league" so to speak, or do they "settle"?