I think Alpha was the most popular on my college campus... followed by Delta.. Phi is up there pretty high for us too.

we had:
Alpha Sigma (local)
Delta Zeta
Sigma Sigma Sigma
Tau Phi Lambda
Delta Omicron ---there's an Omicron for you!
Phi Mu Alpha
Pi Kappa Alpha
Phi Chi Epsilon
Delta Chi
Phi Sigma Kappa
Lambda Chi Alpha
Tau Kappa Epsilon
Alpha Phi Alpha
Delta Sigma Theta
Zeta Phi Beta