Ninjas. Definitely Ninjas! But woe onto both of them if attacked by puppies! Those guys take no prisoners!
It depends on the circumstances. If it comes down to small swift raids on each other, then the ninjas have it all the way. But if it's a full-on fight, the pirates will win. As Ba hopes most people know, ninjas did not, generally speaking, flip out and kill people. They relied on stealth and guile. Once robbed of the element of surprise, they weren't nearly as much of a threat.
