I've said it before and I'll say it again. The best thing any rushee can possibly do going into Rush is to have general knowledge about each sorority (their mascot, their philanthropy, etc.). Your rush manuals should give you that info, but visiting national headquarter websites is a good tool also. By knowing a little about the sorority, it shows the sisters that you cared enough to do some research.
BUT, the most important thing about Rush is to go in with a completely open mind. Don't listen to folks giving you their opinion about the girls in each chapter. (No disrespect meant to daisyflower here!)
Instead, listen to your heart and, by doing so, you'll find the house where you fit the best. Trust me, even with a Greek population as large as UA's, you'll be able to figure out which girls you have the most in common with. They may be the most "popular" on campus, or they may be a small house that just happens to have some really nice girls.
Size isn't everything and popularity CERTAINLY isn't - because people define popularity in so many different ways. It's like trying to compare apples and oranges. Hope this helps and Good Luck with Rush