Hold on there! According to googlefight, it's Ninja, Pirate, Samurai! Ninjas are almost more than the other two put together though.
Stats:
Ninja: 12,700,000
Pirate: 6,940,000
Samurai: 5,780,000 results
I think we can thus see that the ninjas are by far the best!
Source:
Googlefight!