It depends on what aspect you are referring to In the aspect of power a Ninja would win in a one on one battle due to his/her adept training. In the case of a Ninja vs a Pirate the pirate wouldn't be alone so after loosing a couple of his buddy's the Ninja would be taken out but thats only if the Ninja lets the pirate see him.
In the aspect of fun it depends on the individuals insight, Some would find it fun to be a Pirate killing, plundering, raping, Ect. But I would much rather be in some secret organization dedicated to killing in the name of some feudal lord (I'd prefer to be that Lord but thats besides the point.
So I deduce that a Ninja POWNES.