Alright well we need to do some quasi-scientific bullcrap report on the efficiency of their weapons first. Just like Deadliest Warrior really.
But personally I vote... 16th century Imperial Knight. The Gothic Knights from M:TW2. I dunno but I honestly think a Ninja would have a lot of trouble there. And well, I'm anti-guns. The gun ruined warfare in my opinion. But I've always been told that I was born in the wrong century.
EDIT* Screw it I'll vote Pirate. Only cause I think Ninjas are overrated. And I like Jack Sparrow.