I currently have two pets, and keep an open slot in order to get new skills, since im not 70 yet (barely 45).
One is humar, the level 23 elite near barrens. Just so you know, I think (call me crazy, or a RPgeek) the rare mobs have those special skins and names for a reason, and they deserve to keep them, besides they are cool most of the time, so I just rename them to their original names when I tame one. Thus his name is Humar.
The other one is the unique raptor Goreclaw from Dustwallow marsh. A lot of people dont even know he exists, and not everyone has it as a pet, and I just love the way he looks. He is the only non-OL raptor that is black, and quite frankly, I hate the way OL raptors look, its like "LOL HAY GUIZE IM BARNEY!".
I will probably use the 3rd slot on one of the white owls from winterspring, or the color-shifting ravager.