Why is 0 Kelvin absolute zero and why do electrons conduct best?

Answer

The electrical resistance ultimately comes from the interaction (say collisions) of the electrons with the lattice ions in a metal. You can compare it with the ball in a pinball machine. As the temperature increases, the lattice ions will vibrate harder and the impact of a collision with an electron will be greater.

However, you cannot immediately conclude from this that the resistance would be zero at absolute zero: impurities in the metal lattice ensure that a finite resistance remains. There is one exception and that is the superconductors, but that is another story.