Take two guys who are exactly the same in all respects except one is more muscular and women will want the one that is more muscular. Of course, most won't say that because either A) They feel like a guy like that is out of their league and are intimidated by that, so they choose the smaller one so they have more power in the relationship or B) they don't want to seem "shallow" so they choose the less muscular one. Women are attracted to power, and being bigger and more muscular than another guy is just another type of power.