So we all know Vanilla is super duper easy, pretty much everyone can create a new toon and smash people with him right away.
But when it comes to truly "mastering" a class (or playing it very well), what are the ones that are the most skill-intensive ?
I could be totally wrong but from what I've seen I would say:
Tiers 1
Rogue
Mage
Druid
Tiers 2
Warrior
Hunter
Priest
Lock
Shaman
Tiers 3
Paladin
Now to be honest I have never ever played a Shaman and they actually may be easier to play that it looks like but I believe really good Shamy players are able to really use the full potential of their totems.