Originally, I leveled a few pets just for looks... then realized they didn't work as a team, and I was getting roflstomped by the last few Northrend tamers. Then I sat down, looked some stuff over, and made a list of ten pets (one of each family) I figured would be able to take down any team, just by pairing "hard counters." I leveled those to 25 (and used stones to make a few of 'em rare)... then slowly started leveling other 25s to have more options. As a plan, it seems to work well.
The four I seem to use the most are Flayer Youngling, Rapana Whelk, Effervescent Glowfly, and Fel Flame. Some of that is their abilities; some of that is what they can hard counter.
Crabs and Frogs have yet to seriously let me down, Emperor crab is my buddy.
Infectionate Serenades Bubblesbee[A] ↑ ↓ [H]
Nasturtium Fisticuffs Blesshu Sinnocence Shoctologist Ellipsis Hiddenfee Teddiursa
Some of my favorites:
Celestial Dragon. This guy is a real trooper with breath, ancient blessing, and moonfire.
Gilded Moth. Gotta have flying damage!
Pandaren Monk. Hard hitter with humanoid dmg.
Strand Crab. My go-to for aquatic dmg.
Personal World Destroyer. My first 25, still rocks teams backlines with quake and repair.
Cinder Kitten xD
Once you level it up, of course.
So far I have been using the Cornish rex cat as my main trainer. Has high attack and okay speed, and just steamrolls through all the critters. With the high attack it makes Devour a really good heal. Though Cornish rex cat only comes in 'uncommon' quality (before battle stone) it's still a really good pet to train with.
The best combo for powerleveling other pets to 25 is magical Crawdad and fluxfire feline. If the FFF gets low, switch to the Crawdad pop wish, switch back to FFF, continue destroying things. If its a critter or flying pet you are fighting just hit supercharge before using windup.
I've been doing this for a while now in kun lai summit since most packs are beasts with some random critters and flying pets mixed in.
My favorites so far:
Personal World Destroyer
Spiders are some OP shit
Just got a rare minfernal thanks to a awesome CRZ trick posted on wowhead (minfernal's page comments) and i got to say. Hes isnt very good. The magic type helps him out a bit (it would take at least 3 hits to kill him) and he has an ok move set but nothing to rave about.
I guesss a moonlight based team would work with him, need a decent healer (Magical crawdad) to keep him going.
"Humility defeats pride, Master Yang has preached. Pride defeats man"
I run triple fluxfire feline in PVP battles. Haters gonna hate.
For leveling I use 1 fluxfire, 1 anubisath and low lvl pet.