These are the best hunter pets for arena, battlegrounds, 1v1 duels for both current viable specs, Marksman and Beastmaster.
This is based on personal opinions. For arena as Marksman, the best pet is the monkey since it has a 4 seconds blind that will help the CC chain. Also it can be played with a wolf or cat for the buffs if is a triple dps comp or an easy comp. Before the arena starts, a cat or wolf can be called for buffs, dismissed, then summon the monkey or spider. Spider is also an option when trying to catch enemies using web. Still 90% or even more of the hunters that are doing 3v3 are using a monkey.
For battlegrounds probably the best pet is the scorpid since it has a 10 seconds disarm and Intervene that can save around 60 to 90k dmg taken. Is great against rogues, ferals and great since many players don’t use the weapon chain enchant meaning that they will be disarmed for the full 10 seconds.
For 1v1, depends what class the duel is against but mostly monkeys are the best since they can interrupt casters and blind rogues, warriors, etc.
For beastmaster, arena, the spirit beasts or devilsaurs that got -10% health received debuff will work. In duels, the same, spirit beast with heal will do the job.
In battlegrounds either a spirit beast or a core hound for heroism will be fine. The easiest spirit beast tame is the bear from Grizzly Hills since it has just one spawning spot.