Diablo – Which Attack Spell Hits the Fastest

The spell best suited for this is Shock Pulse with the rune Living Lightning.

The spell has an insane amount of hits/second, however each hit deals low amounts of damage , but it adds up to the same DPS as any other spell doing the same amount of weapon damage percentage.

Combine Living Lightning with items that improve Attack Speed and you will fire an insane amount of attacks per second, with each attack producing lots of hits/second. If you fire off several Living Lightnings, you will regenate 5 Flashes of Insight in a few milliseconds after you've casted your non-signature spell.

The skill: http://eu.battle.net/d3/en/class/wizard/active/shock-pulse
A video showing the skill in action:

They use Shock Pulse and Living Lightning with a rune that reduces cooldowns by 1 second for every critical hit. You gain lots of critical hits with Living Lightning without critical hit gear, imagine what you get if you gear up correctly!

NOTE: I am not sure the above build works anymore, changes were made recently, but Living Lightning was unaffected.

Yes, that is the basic weapon attack. When you start out a level 1 character, it's the skill that is on right mouse button. With wands it's a small projectile, with swords you would run up to the monster and slash it.

You can also set this skill if you are in elective mode, and assign a skill to a hotkey when it is already assigned. For instance, if you have Magic Missle assigned to left mouse, and decide to remap it to right mouse, you will get the default weapon attack set to your left mouse button.