I pretty much agree w/ all the replies. Yeah, a chapter would probably extend bids to both girls. But to be honest if it came down to one or the other and they were equal in every single other trait; the pretty girl would get the bid. Fortunately you'll never find two people who are identical in all other traits.
It's also true that like begets like. A chapter full of pretty girls will attract other pretty girls. Money attracts money. Brains attracts brains. The only thing I waiver on is if this is because the pretty girls only want to associate with pretty girls or if like Allie said, they just have more in common.
Personal appearance is something that we take into consideration during formal rush. It's not ignored during informal but it's more subconscious. In my chapter though, personal appearance falls more into did she shower and make an effort to look nice or did she run right over from the gym.
I know for a fact that our chapter at State puts much more emphasis on appearance. But that's how their entire school is. They actually turned down a legacy because she wasn't pretty enough. I happened to meet the girl later and she's cute! Just not pretty.
Personally I think it's up to each rushee to determine if this kind of thing matters to her or not. When I went through rush I spent hours getting ready each night for the parties. Then the next day I'd roll out of bed, put my hair in a ponytail, wear my glasses instead of contacts and go to class. I knew there were members in my classes. But I didn't give a @#$%!
Honestly, I believe this led me to not get a bid from the other house I wanted.
But now that just makes me feel sorry for the girls in that house.