The ones that have presence (Alpha, Beta, Gamma, Delta, and Epsilon) are all the best. My particular favorite is Beta, but especially when she's "fighting" with Epsilon (the boob size rivalry is largely one-way, Beta is generally oblivious about it). Beta is also the most vicious to Alexia and the other girls outside of Shadow Garden, which is very funny to me.
Zeta is only good for cat gags imo, and Eta just has zero presence at all.