I've been using:
Onyxian Whelpling (Tail Sweep / Healing Flame / Lift-Off) vs. his magic pet. Lift-Off instead of Deep Breath, since it can only do 40% of the Eye's health in damage, and it also lets me shave off a turn of it's power debuff it uses while also avoiding one attack. Even if the Lift-Off misses, the Tail Sweep makes quick work of it. I don't bother healing, instead, I try to get a hit or two in on the next pet with the Dragonkin buff active for a headstart.
Searing Scorchling (Burn / Immolate / Conflagrate) vs. the mechanical. Start with Immolate to get it burning then Conflag. This is so one-sided the Conflagrate will sometimes knock it down with the first hit, it repairs, then the second hit kills it for good.
Darkmoon Tonk (Missile / Shock and Awe / Ion Cannon) vs. the Monkey. This guy just completely destroys beasts and this is no different. One thing to note: If the Shock and Awe stuns the monkey, it'll be swapped out (unless it's his last pet) before you can hit it again.
Of the pets I initially leveled to 25, these were my best choices to bring in against this team. I was a little worried, since I hadn't actually battled any of the trainers with epic pets up to this point, but I've one-shot this quest every time so far.