Loreli-
That is a legitimate question, however, you should NOT choose a sorority based on stereotypes or what other people say/think about them. Use your own judgement in choosing the place that is right for you as opposed to becoming partial to any one of them because a friend or aqquaintance likes them.
Are you thinking of rushing in the Spring or Fall? What type of recruitment does your school hold during the season you intend to go through? Rules vary depending on whether the rush is Formal or Informal. Formal recruitment rules are very strict, and if you go through this type of recruitment, you will most likely have to visit all of the houses at least once.
Keep an open mind & don't listen to rumors. Even different chapters of the same National sorority vary in the personalities and interests of their members depending on the school. For example: just because a sorority's chapter in one state is known for being athletic doesn't mean all the others are great at athletics also.
Visit the National and/or local websites of the sororities on your campus & read about each sorority's philanthropy (a special cause they donate time & money to such as cancer, aids, abused children, etc.), each sorority's mission statement/ideals, and things such as what sisterhood means to them. These are the most important factors in choosing a sorority.
A good starting point is
http://www.npcwomen.org
This is the website of the National Panhellenic Conference, of which all three of the sororities you mentioned are members.
Also, talk to someone in your school's Greek Life office to get the details on when recruitment is, etc.