Turmoil is good for general Bossing, Slaying, PKing etc.
Piety is really only good if you can get overloads (And not have overloads w/ Turmoil) and are a pker, as your combat is lower, which means u'll be fighting mains with turmoil with much lower combat stats, giving you the advantage.
All-in-All, i'd get turmoil. SS + Turmoil + Berserker helps ALOT in any situation.
Turmoil and Overloads absolutely rape. It's well worth it dude.

