Two-Step Goodbye or greased lightning

That all depends. Are you going up against one enemy at a time or groups?

in general as a standered unarmed weapon

They're both good but I like some of the unarmed weapons from previous DLC better (Industrial Hand and Saturnite Fist Super Heated for my Pyro).

Greased Lightning will drill its way through most things without much trouble. The Two-Step is situational. If you're in close quarters it can be more dangerous than it's worth until you've got a little experience with it.