Play a Healer if you want to learn positioning/cc/mana/dispels. That will help you.
Nothing is 'the easiest'. It's all about the player, not the class. I find Resto Shaman easier than my Mage, yet a friend of mine is great on his Mage but awful on his Rsham.
You have to play everything or at least play against everything to stand a chance of learning anything.
Also, I don't agree with that list posted lol
Warlocks are amazing at high ratings due to the fact they are quite hard to play amazingly.
Enhance is hard to play well. Druids are easy. Resto doesn't count cos they are broken atm.
Priest should not be above rogue lol
TL;DR - Play a healer. You will learn so much. People tend to tunnel like derps if they pick up a DPS