Of those? Penguin is rich, so I'd actually have a chance of getting paid, and he's not an out-and-out psychotic in most incarnations, so I'd have a better chance of not getting whimsically killed off, and most of his crimes are about money rather than proving he's smarter than that black-bedecked-bat-brain or love of chaos or hatred of humanity or (etc. etc. etc.) so there's a much greater chance I'd continue to get paid rather than getting sacrificed for my boss's cause.
Of course, first time something goes really wrong on a mission someone's going to take the fall, but I think that's pretty much the case with any of 'em. Mission goes south? Time to leave town.
Pity Catwoman tends to work alone.