Spartans were extremely tough no doubt. But they fought as an army. Ninjas specialized in killing multiple enemies as silently as possible.
In a true 1v1 the Ninja would win because the Spartan would not have his buddies watching his sides and rear. The Ninja is just to fast and tricky for the big slow Spartan. Don't get me wrong, Spartans are cool too.
Shoulin vs Mauri - another example. The monks won as they should, but the Mauri are simular to the Spartans.
Terrorists vs Terrorists? Are you talking about the Taliban vs IRA? If you are, , the IRA are not terrorists, they are Freedom Fighters. They fought to free their own country from outsider oppression. That is not terrorism, it is courage.