most popular sororoities

Depends what kind of popular you're looking for.
If you care mostly about looks, getting drunk and high on the weekends, and hooking up with guys in frats they're friends with: Pi Phi, DG, Alpha Xi Delta (although they've actually lost a lost of popularity over the past few years) and Alpha Phi (not trying to be mean, some people really like this type of popular)

If you're looking for good looks and high reputation for that but a catty sisterhood, Kappa Kappa Gamma

Popular for being well liked by most sororities and fraternities because they're easy to get along with, are generally sweet/friendly people, have good sisterhoods, and are cute/classy: Delta Zeta, Alpha Chi Omega, and Kappa Delta

Nice girls but not popular: (and these people stalk this website so you'll know it's them when they comment how rude and wrong and and crazy this is): Chi Omega, AOII, and Sigma Kappa