I'm so happy that you've been invited to join our sisterhood!
I guess in deciding between the two groups, is there one that you feel more of a connection with?  Do you feel like you have more in common with the members of one group than the other?  For example, I visited two chapters while a PNM.  One had women in their 30s and 40s, the majority of them had kids.  They were nice, but I really couldn't see myself in the chapter.  The other chapter (that I eventually joined 

 ) had members in their 20s and 30s, some were married, some single, some with kids.  I felt like I fit in better with this chapter.  Sometimes you can just tell, you know?  I guess the big question is, with which chapter do you see yourself fitting in with the best?
Hope I don't sound like a bumbling idiot.  If you want to talk more, you can PM me.  I can't wait to hear your decision!!