The easiest and simplest class to play?

[GnomeCaptain]

Monk is vastly simpler than Mage, Rogue, or Wizard.

On the latter three you have to be careful about agro.

In my experience very few players of these classes maximizes their damage and utility to group. Most rogues go too far; few Wizards understand how to optimize their CC and dps.

But with a monk it doesn't matter all that much if you get agro, you're pretty tanky and can fd anyway.

If you explore and take a wrong turn, fd.

And you don't have to worry much about getting weapons or armor. And because of weight-restrictions many other decisions are made simple.

It has to be the simplest class by far.