Lil' Deathwing is a beast in PvP...Netherwhelp is a lot of fun in PvE, but for some reason I have never used him in PvP yet haha. Because of this thread, I will give him a try!
Also, I like Grommloc a lot too with the fun comp I setup with Yu'la, and Mini Diablo. Its fun, and people never see Mini Diablo in PvP pet battles. I setup with Yu'la and use Celestial Blessing for the swap to Mini Diablo. He can take some hits, and deals out good damage. Grommloc cleans up the trash, and its a fun comp I like using.
I use the Panda Bear (CE pet) for one of my bleed teams. What other Blizzcon/CE pets do I use for PvP...oh that's right....Frosty!!! Awesome pet in PvP and I love using him