http://www.wow-petopia.com/This will be your friend from now on. There are 3 types of pets, tenacity (for tanking), ferocity (for raids, dps), and cunning (suppose to be for pvp but for dps aswell). There are no difference between two ferocity pets anymore. The only difference is the buff that those pets give.
If you can't find something on petopia then feel free to ask. I'd go with cat btw, kinda pointless to have a tank pet with the dps boost that every single class got.