Let's set things straighter:
Calymores [and all the other heavy two handed swords] are for fighting mounted and the fighting consist in swinging once at your enemy and hope to deliver a blow [which will be fatal or at least will injure the oponent that badly that you'll be able to kill him by slapping him].
Main characteristics: Blunt damage, slash damage.
You don't use claymores for close combat unless:
a) You are a retard
b) You have a death wish
c) You are incredibly strong
Swords can come in a large variety of shapes, sizes and weights, and they are designed for close combat. And, yes, Xordan is right, there are swords that have very low weight and can be handled with a great speed.
Main characteristics: Slash, pierce, blunt damage.
Knives and daggers... Well, better than those, use a bow or crossbow. In close combat, as Xordan said, you don't want to use them unless you are fighting somebody that doesn't have a "longer" weapon than you. Good for backstabbing but if you are planning to fight a sword fighter with knives... well... apply points a and b from claymores.
Main characteristics: pierce damage [the slash doesn't count because of the short blade]
And now to Zanzibar's original point:
Swords can _easily_ kill in one blow. For knives... well, it is more difficult because you need to aim for soft vital spots. And if you consider the lenght of the blade, the shorter the blade, the fewer the spots. With a sword, especially with a medium weight sword, like a katana or odachi, you have a plentitude of vital spots to chose from so, your chance of delivering a fatal blow is increased.
In conclusion:
Don't play with knives.
Don't run down the stairs with pointy objects in your hands.
Don't run at a guy holding a sword with a knive in your hands. [The direction of the running should be opposite, actually]
Don't bet your life on the fact that the guy with the sword will spin for 10 min after swinging the weapon.
