honest opinion

I truly don't believe USD has a definitive "ranked" system. I think it's more accurate to rank people by tier level, because the "top house" preference is going to change from person to person.
THAT BEING SAID (tiers in alphabetical order)

Frats:
Delt/Fiji/Lambda
Phi Kap
Beta
Sig Ep/Sigma Pi/Pi Kap

Sororities:
Aphi/Gphi/Kappa
AXO/KD
Theta
ADPi/Pi Phi