tier system

It's supposed to be based off of popularity, but obviously that isn't necessarily correct because popularity is subjective. Traditionally the more social/parties an organization is/has, the higher the tier. Again, subjective. Many people are not interested in top tier because they feel more at home with a different type of person. Bottom line. None is better than the other. Don't worry about tiers, just find what feels right to you. And, oh, after Freshman year no one really cares. I was in a so called top tier and had friends in many different tiered sororities and loved them equally.