Been a few days, so I don't feel bad about double posting:
Aside from purchased ones and a few others, most Battle Pets have multiple potential builds. They either gain a LOT in one specific stat (health, speed, power, or balanced); some in one or two; or are balanced pets.
Considering these hidden builds are more important than anything, now that you can upgrade a pet's rarity with Battle Stones.
So, if you're serious about getting a leg up on Pet Battling, this addon <a href='http://www.curse.com/addons/wow/battle_pet_breedid' target='_blank' rel='nofollow'>Pet Breed ID</a> and <a href='http://wow.curseforge.com/addons/battle_pet_breedid/pages/what-is-the-breed-id/' target='_blank' rel='nofollow'>this guide</a> might be very helpful to you.
Some tips for those who are struggling with pet battles:
Some Aquatic pets (like <a href='http://www.wowhead.com/item=84105' target='_blank' rel='nofollow'>Fishy</a>) get Cleansing Rain, which heals all party members for the first round it's active, and helps Aquatic pets deal most damage.
The Black Lamb also has a full party heal.
The Onyxian Whelpling, as well as Lil'Onyxia, the Corefire Imp, and a few others get a self-heal that restores an amount of health, plus half of the last hit taken; which is quite useful at negating some of the damage flung by heavy-hitters.
If you're looking to neutralize the advantage of the self-heal, you can use multiple-hit attacks, such as Flurry, Nut Barrage, Swarm or Stampede; the two lattermost also breaking their defense.
To counter Flurry, Nut Barrage, Swarm, Stampede and other similar abilities, there are counters like Immolate, which throw back damage every time the user is hit.
Pets with lots of DoT damage, like the Jade Oozling, can put out a frightening amount of damage against the unwary.
I'd strongly recommend trying to get a Terrible Turnip, as frustrating as it might be, as it has "Weakening Blow", which can harm, but never defeat, an enemy by itself. You can use this to tear down an enemy for capture, or use it to power level weaker pets by beating the enemy down, then having the turnip suicide, and leave the pet you want to level to do the last point of damage for the match, thus claiming a ridiculous amount of XP.