Battle Pet Tamers: Kalimdor

Five trainers make up the quest line for beating master pet tamers in Kalimdor and these tamers all use different pets from magic pets to mechanical pets to beasts and critters. Various zones in which these tamers hang out include Feralas, Dustwallow Marsh and Felwood.

There have been some reports that doing these quests as an Alliance character won't properly award credit for achievements and quest completion and this issue might even get in the way of further questing for beating the pet tamers throughout Azeroth. This means it's recommended that this quest be completed on a Horde toon if possible. For anyone without a high level Horde, leveling a Death Knight for this purpose is easy and just takes a few hours.

Traitor Gluk

Traitor Gluk is located in Feralas

Traitor Gluk is located in Feralas and has a Beast named Rasp, a Dragonkin named Glimmer and a Critter named Prancer. All of Gluk's pets are level 13. To beat his pets with low level opponents, you'd be well set to choose:

A pet with Mechanical abilities to fight Rasp the Spider.
A pet with Humanoid attacks to go up against Glimmer the Faerie Dragon.
A pet with Beast attacks to go up against Prancer the Fawn (well, perhaps he's a reindeer).

Grazzle the Great

Grazzle the Great is located in Dustwallow Marsh

Grazzle is located in Dustwallow Marsh and is right near the spawn point for the heavily farmed Spawn of Onyxia pet and the entrance to Onyxia's lair. He has a trio of mini Dragonkin named Blaze, Flameclaw and Firetooth and his pets are all level 14. If you'd like to level up against this tamer, you'd best use pets with...

Humanoid abilities which will beat up on his minature Onyxias or pets that don't take a lot of damage from Dragonkin abilities (such as some Undead pets) as Grazzle's pets are apt to cast Scorched Earth. You can also think about using a pet that changes the weather to something more accommodating (like Moonlight).

Kela Grimtotem

Kela Grimtotem is located in Thousand Needles

Kela is located in Thousand Needles and is on one of the mesa tops in the middle of the zone. She has a Critter named Indigon, a Critter named Plague and a Beast named Cho'guana which are all level 15 pets. The best adversaries for these pets would be:

Some pets with Beast damage to go up against Indigon the Beetle and Plague the Rat along with a Mechanical pet to go up against Cho'guana.

Zoltan

Zoltan is located in Felwood

Zoltan is located in Felwood, home of the elusive Minfernal and anyone who might want a Minfernal will be particularly jealous of Zoltan's pets since he seems to have a minature Supremus, which was a boss in the Black Temple instance a few years ago. 

Zoltan also has a group of cultists surrounding him, so his pets must be particularly popular with the locals. Zoltan has three pets that are fairly difficult if your pets are the same level and it can take a bit of time to defeat him if you don't otherwise bring the right pets that can do a lot of damage to them.

Zoltan's pets are all level 16 and his first pet will be a Mechanical named Hatewalker, his second pet will be a Magic pet named Beamer and his third pet will be another Magic pet named Ultramus. Should you wish to down Zoltan's pets with ease...

Consider bringing a pet with Elemental attacks to defeat Hatewalker the minature XT-002 Deconstructor (from Ulduar). 
A pet with Dragonkin attacks to beat Beamer the minature Eye of Culuthas (and Mists of Pandaria era warlock pet). 
And another Dragonkin type pet to beat Ultramus the miniature Supremus (let's hope the developers like this tiny model enough to offer it to players in a future patch!)

Elena Flutterfly

Elena Flutterfly is located in Moonglade

Elena is located in Moonglade and she has a Dragonkin named Willow, a Magic pet named Beacon and a Flying pet named Lacewing. Each of these pets is level 17. Should you want to use Elena as a leveling tamer for your own pets, you can choose:

A pet with Humanoid abilities to go up against Willow the Dragonkin.
A pet that uses Dragonkin attacks to beat up Beacon the Lamp (yes... it's a lamp... a magic lamp!).
A pet that uses Magic attacks to give Lacewing the Moth a hard time.

Should you beat all of the tamers that this Kalimdor quest has to offer, you'll next go up against Grand Master Pet Tamer Stone Cold Trixxy who is located in Winterspring. 

The fastest way to get Battle Pet Tamers: Kalimdor completed is to start in the south and work your way northward since after you defeat the last tamer (which should be in Moonglade), you'll be automatically given the quest for Stone Cold Trixxy, which is just a short hop over the mountains into Winterspring.