Haven't really bothered about leveling that much through wild pet battles, but last I did it to get the last few xp on my lvl 24's, here is what I did:
Kun-lai summit (lots of critters and beasts, especially if you find a tolai hare / hare pup family toiling around).
Used these pets:
- Flayer youngling  vs critters (triple snap, reflection, rampage)
- Darkmoon tonk vs beasts (missile, shock and awe, ion cannon). Particularly rewarding when the last pet is a beast and to oneshot it
Of course have the safari hat on.
I still prefer doing tamer dailies as to not get totally burned out. But that strategy is a pretty decent one. Bear in mind that the level range in Kun-lai is 23-25. To ensure highets possible level on enemy pets for xp purposes, try vale of eternal blossoms (level range 24-25). Loads and loads of aquatic pets there. I suppose a Gilnean raven , Yellow moth  or an Effervescent glowfly  should serve you well there. A proto drake whelpling  for any fliers + its awesome self heal could perhaps be a backup pet.