To elaborate on the pets...
Pets fall into 3 categories, which each give a respective buff. Or no pet.
- Cunning - 8% movespeed
- Ferocity - 10% leech
- Tenacity - 5% HP and an active that reduces dmg to you and your pet by 20% for 6 seconds
- Lone Wolf (no pet) - 10% damage increase
Typically, Lone Wolf is going to provide the best damage for marksman. It isn't an option for BM/Survival. That being said, you'll still want a cunning pet on you to summon when moving around in BGs (coming back from GY, moving to an objective, running the flag). A tenacity pet is also a good option if you end up holding the flag. Ferocity can be ok if you constantly have it out while fighting for some health regen, but usually the damage is too much for it to really matter IMO.
Beyond that, there are 6 abilities that pets can have. Defense, Dodge, and Triggered Defense focus on your pet's survival - which are mostly only useful PVE. Theres a Tranquilize/dispel that you don't get until higher level, so we can ignore that. Which leaves us with Mortal Wounds (anti-healing debuff) and Slow.
A super helpful chart showing each pet type and the respective family and ability can be found here:
http://wow-petopia.com/abilities.php
IIRC, hunters only have 2 stable slots at 20. So you want one mortal wounds and one slow. At least one of those should be cunning. The other can be tenacity if you expect to hold the flag, or also cunning because movespeed is just too good.
So I'd choose 2 of...
- Cunning w/ Mortal Wounds - hyena, raptor
- Cunning w/ Slow - Basilisk, Birds of Prey (owl, eagle, parrot, etc), Dogs
- Tenacity w/ Slow - Crab
You could also play around with ferocity, though I think its better for BM/survival.