[Denise_DPhiE]

First you should make up a list of questions that YOU have for the groups. Decide what is moat important for you to know about them in order for you to decide if they are right for you.

Philathropy Projects (national and local projects)
Programs and activities
Requirements of new members and actives
Dues and fees

You can always ask a sister "Why did you join" or "what is your favorite part about being a XYZ?". This gives you a chance to deflect the conversation, get your bearings and maybe some extra info about what being a sister is all about.

Good luck. I would also suggest attending parties for all groups who are doing informal - it sounds like you have already made your mind up for 2 - give everyone a shot - the worst thing that can happen is you get cut but you might make some new friends in the process.