POINT BY POINT!
Bigger:
Zombies are rotting and getting smaller all the time by rotting/dismemberment. And they are not the life of any party.
Pirates were all for glory and plunder. Loud proud and clothes that would make a pimp look unpimp.
Ninjas are neither loud nor proud.
Conclusion: Pirates are biggest.
Baddest:
Zombies shuffle around in mobs never moving very fast, true they have the cannibalism thing going for them but they gotta eat.
Pirate sacked entire towns, sunk entire fleets, killed their best friends and tortured for fun and profit.
Ninjas have all that code of conduct shit holding them back.
Conclusion: Pirates are Baddest.
Ass kicking:
Zombies alone are not hard to take down, besides they fewer to chew their ass.
Pirates: Sabres, rapiers, cutlasses, pistols, muskets, musketoons, blunderbusses, cannons, and belaying pins. They lives for the fight and the rewards it brought.
This is the only place ninjas would really excel, though they light have to get the jump on a pirate, which is what they were good at.
Conclusion, pirates and ninjas would have a hard time with eachother.
So with 2 out of 3........ <.<