1: Pirates got their own accent.
2: Pirates are free, ninjas are not.
3:Pirates got Alestorm!
4:Pirates got larger parts than ninjas in History, both IRL and in WoW!
5:Pirates got guns, ninjas got katangas. Guess what wins.
6:Pirates can travell to any land they want, because they got ships. Ninjas dont got any ships!
7:Ninjas can only attack people when they are sneaking, or from behind. Pirates can attack from any distance!
8:Pirates got nice hats.
9:Pirates excist(ed) all around the world, Ninjas only in a few places.
10:There excists ghost pirates, but no Ghost Ninjas.
11:You can actually see pirates.

This is why pirates are more awesome than ninjas, folks!
(Jokey thread inspired by the Tauren are better than Worgen/Night Elf better than belf Thread!)