If casters are giving you trouble, then the core hound is the exotic pet for you. Their Lava Breath ability slows down the enemy's casting speed by 50% for 10 seconds. The cooldown is also ten seconds, so you don't even need the Longevity talent to keep this up all the time, which is especially nice for PvP also. Their Ferocity talents give them lots of extra damage and self-healing options as well.
The core hound is the pet with the loudest footsteps in the game -- their feet pound the earth so hard it even makes everyone's screens shake if they happen to be nearby. So if you're the kind of hunter who likes to announce to the entire world, "Here I am! Look at me! Right here!" then this is the pet for you; but if you want to be sneaky and avoid attention, then you ought to look elsewhere.
BRK loves core hounds lots. There are three types to choose from: red hot, green hot, and white wolf; found in Blackrock Mountain, Shadowmoon Valley, and Azuremyst Isle respectively.
If you want a non-exotic alternative to core hounds, you could consider the serpents and their Poison Spit ability, which is almost just as good as the core hound ability, and ranged too! You won't deafen people and shake their screens with a serpent, but you'll do the trick just as well, more or less, especially if you have Longevity. Serpents are Cunning pets though, so you it also depends on which talents you prefer.