Samurai are extremely over-rated, and werenot nearly as good as people make them out to be. Their swords weren't amazingly durable and sharp - at least, no more so than european steel.
Knights on the other hand tend to be under-rated. People tend to think fo them as being this big, burly, slow lords who could die form a single stab wound, when in reality, qhile being limited by their armour, they were extremely well trained and their armour could protect them from most swords, which is why many were taught hoiw to use "half-handing" or "Half-Sword" - the technique of holding the blade in the left hand and using it as a thrusting weapon to drive the point into weak spots on the armor. Along with that, the sword could be held by the blade swung like a hammer, using the crossguard to damage the enemy's armour.
Vikings...well, vikings are from a different time. Their time ended around the time of the Normans, I believe. I'm fond of vikings, since Ireland has numerous cities that are of viking origins, but I'd prefer the later eras.