the Death Knights, but with all the spotlights on the DK, there are classes that became broken beyond playability. For example, the Hunter. The hunter who relies on his pet to do some of the damage and take some of the threat is done, unless pets are fixed. It's great that they changed the way pets gain skills but somehow in the patches of the private servers, the pets never learned how to eat. Pets who do not eat get pi$$ed off at you and run away and then you have to find another pet.
Of course you can say that you can be a hunter without a pet. Sure you can but if i wanted to be a hunter without a pet, I would be a rogue or warrior.