Ok.

I've not been talking about viking berserkers, I'm just going to make that point clear. Viking berserkers more often than not wielded small axes, ones they could put they're strength behind to slice off limbs of common foot soldiers. More often than not, they would wield two axes, slightly larger than a throwing axe, so that they would be light enough to not overly tax the berserker's stamina.

A knight of the times when they where at their height where nearly unstopable in battle, which is why they where able to aquire keeps and castles at the head of their armies.
A knight's steel plate armor was fitted over a chain link undershirt that deflected impact force, and kept the sharp point of an object from injuring the knight if it slipped between the plates. Another common misconception about a knight is that the armor left large holes in their defense. This is wrong. The armor was desinged specificaly to be impenatrable to attack, why would they leave weak points in it?
The best armor where made from steel plates of extremely high grade, more often than not they where better than their swords. The full plate armor weighed in at several hundred pounds of solid steel. And it fit perfectly to their bodies, they would sleep, eat, walk, and pretty much live in their suits until battle was done.
Knights where incredibly mobile in their suits, and more often than not had much greater strength than the average man for having to constantly hike around several hundred pounds of steel, being extremly well fed, and being allaround fit. A knight's only difficulty in battle was progressing uphill. And getting on a horse -_- That was a real bitch for them.
Also, on a final note, even though their armor was immensely heavy, a large portion of the weight is distributed down to the feet, so the knight was only actually moving around the weight on his arms and legs, the vertical weight [such as the helm and breast plate area] where distributed so that very little weight had to be carried by the knight.
And, again, the armor was actually more protected at the joints than along the length of, say, an arm. The joints where wrapped in interlocking plates of thick steel, and where incredibly well fitted. It's next to impossible to slip anything into the gaps left inbetween the plates, and with multiple plates, completely futile.

So, on to samurai. I know little about their fighting style's and their armor, but I know a great deal on the swords.
The average japanese sword is very crummy, because the ore's and minerals the swordsmiths had to work with had many impurities, and other varied reasons lead to the fact that the average sword would easily snap on the most simple metal armor, and wouldn't have a chance of penetrating chain link.
On the other hand, the technique of making damascus, an alloy of steel and other metals, makes some of the best bladed weapons in the world. In fact, their are examples of damscus blades being stronger than the highest quality laboratory produced alloys. This is because damascus turns impurities into strength. A damscus blade is created by taking sheets of different metals, and pounding them together, over and over and over, untill they've completely fused. Then you do this again to another sheet. Then you pound these sheets together. And you repeat this process over, and over, and over.

It can take a year and more to create a damascus blade, (or, as it is called in some circles, a "water" blade, due to the distinctive wavy pattern it creatse) but an alloy of damascus can be stronger than diamond.