Just my opinion. (<--- Said to avoid flaming, and debates of class balance (lol) )
But some of the stronger classes/specializations are, Mages, as a whole. Subtlety rogues, Priests, Namely disc. Then anything with above 50% resilience as a protection/tanking spec, least, that was the case, before the removal of pvp vengeance, Haven't played much lately.
The weaker classes/specializations being Warlocks, Hunters, And warriors, In that order, of course, this is just how i see things, Some classes really need abilities, some really need removal of control (Cough, Frost mage, Cough).
And yes, Rogues are very viable.