gamma sig

They're so large that its really hard to rank them. I'd say they'd be a strong middle. The girls are all really nice and have plenty of hot girls in the mix

They are considered an RSO, not a Greek organization. Many girls who are in gamma sig also are in a Panhellenic chapter. I'm not a member of gamma sig so I really don't know but from what my friends basically say (who are in it), it's more of a club.
They also have over 300 members in gamma sig so most people only know approx 50 girls. And they do more community service and less social things. (Since they're a community service organization)
Gamma sigs dues are much cheaper though (because they don't do as much).
Id say be open minded for everything and find what interests you.