I just experimented a little in order to get a balanced group that won't be destroyed by any inconvenient enemy. One team that worked out pretty well is this one:
Fluxfire Feline (S)
Oily Slimeling (with Absorb, Corrosion and Acidic Goo)
Basically the backbone of this team is the Fluxfire Feline - I just wrote a little bit about that little kitty on wowhead - which I can't link since I didn't do 8 posts so far.
wowhead. com/npc=68838#comments:id=1782963 maybe?
A lot of teams get heavily damaged if not destroyed by it, if you make sure you don't waste it on one of the rather few counter pets.
The Oily Slimeling is there to counter burst pets - like the pretty often used Fluxfire Feline. Btw: A Fluxfire Feline just gets destroyed by the Slimeling, since it need 3-4 hits to kill it, depending on the number of Absorbs between the first and last hit.
One thing to remember: If you know the next attack will be a devastating single hit attack, you can just swap in the Slimeling and soak the hit.
The Molten Hatchling is a pretty nice "tanking" pet, that can counter a lot of defensive pets (if they can not deal enough damage to get through the healing), can soak high dmg abilities that have a high cooldown and can just destroy any DoT based pet, like the Oily Slimeling.
Overall I got pretty good results with this team so far, however: Conflagerate is a rather annoying counter, since it deals a high amount of damage in two parts, a) rendering the magic passive useless, b) greatly diminishing the effect of Cauterize on the Hatchling an c) having the potantial to nuke right through the mechanical self repair.