I'm fairly comfortable with every class/spec and it only really takes me a day or two to adjust to a level that feels powerful enough to take on most players. I only feel exceptional at one class at a time though. I can't focus on more than one class properly, but I can play every class to at least an average/slightly above average level.
Unless we're talking about pve, i can play any class exceptional in pve regardless of the role because learning a rotation was never the hard part in PvE.
My main (hunter) I play really well. I have a blood DK which I play I would say just above average. Also got a mage who I am terrible with and a resto druid who I am also really bad at.
I can't master more than one class so I just put most of my time into my hunter so I can continue to perform well xD