What do you use?
Whichever one I consider the best looking at the time. Generally a Hawk or one of those Zandalari Raptors.
But I have the feeling you're looking for answers on which is the best pet to use. You can buff 10% haste before the fight which will last 2 minutes, and I'd say 5% crit is the best buff to keep inside.
I can't think of any reason why you wouldn't go BM and bring a corehound, unless you hate BM for some odd reason.
Assuming you can't get any Blessing of Might or crit buffs, you should get the 10% attack speed buff before match starts then switch to cats mastery, it's the highest damage increase.
Unless BM then corehound ofc.
If you are having trouble with surviving then go bm and use a spirit beast for the heal.
I used Corehound and did rank 1-10 in a day.
My gear is above average though
I usually prebuff with a serpent for the 10% attack speed, then either go with a Core Hound for the Lust or a Spirit Beast for the self heal.
Reached Rank 10 with a wulf and survival spec with 2 exceptions. For Battletron and Big Badda Boom I specced BM and used the Spirit Bond and Spirit Mend (from spirit beast).
Atoms are liars, they make up everything!
BM: Corehound, wolf, serpent, spirit beast, ravager (ravager should really be a shale spider for +stats, but I haven't bothered to tame one)
SV: Wolf, serpent, cat, dragonhawk, ravager
Unless you end up in buff raids, in which case shift out buff pets for debuff pets (-12% armor, +5% magic dmg, +4% phys).
Only one I can recall shifting from that was on the rank 9 bomb boss, swapped to 5x spirit beast. With exhilaration and a herbalism healing potion.