I've only dabbled in it, so my opinion on the matter is clouded by unfamiliarity. But because OSX is sitting atop a powerful kernel, the bourne-again shell seems to me, because I'm more familiar with it, much more dynamic.
In other news, I love logging onto my son's system in his bed room remotely and typing in a shell:
bash$> say daddy says he loves you.
bash$> say goodnight