What is the best pet?

The different elemental pets each have their own advantages and the answer is really, "It depends on the circumstances." Some of the factors to consider are whether you are grouped or solo, is your pet "tanking," what type of opponent you are fighting, where you are fighting, the level of you and your pet, etc. See the section on Pets (Types of Pets for the strengths and weaknesses of each type of pet for more information.