I'm just going to provide an alternate viewpoint. I don't disagree with anything Abbotta or Ranok said, but personally I've used a completely different strategy and I do fine. I don't have a Magical Crawdad, I rarely use multiples of the same pet, and I don't think I have any WoD pets in my rotation, except as carry pets. Again, I'm not saying those are bad strategies or bad advice, just that it's not the only way to go.
First, I think that a lot of people over-emphasise breeds. Certainly, speed is good; being able to go first in a fight means that you get a free attack, so if you have a stun or reach the kill point you don't get hit back. That's great. The thing is, with the exception of the Celestial Tournament most pet battles can be won with a small number of powerhouse teams, and that includes Garrisons, Legendaries, and Trainers. So rather than making sure you have the exactly correct breed of fifty different pets, you can build a few strong teams and just bulldoze everything.
For example, in several Garrison and WoD Trainers battles and I just use a pair of Iron Starlettes backed up with a third chosen to counter one pet; they may be non-optimal, but they can do the job. Alternatively, I may use a Darkmoon Zeppelin and an Iron Starlette, sometimes the timing works a bit better. Mechanicals are generally amazing because of their class ability.
Here are a few pets I'd recommend getting to 25 Rare. If there's a specific breed I've noted it:
2 Frogs (you want Water Jet and Cleansing Rain). Fast is best if you can get them, but you can destroy many MoP trainers even with slow frogs.
2 Nordrassil Wisps, preferably S/S. Low damage, but Blind + Soul Ward means you can neutralise most big hitters.
You may want a second Iron Starlette, but it's not high priority.
2 Spiders/ Crawlers, preferably S/S with Brittle Webbing and Leech Life.
2 fast Foxes or Fox Kits.
2 Moths with Moth Dust. Breed is irrelevant since Flying creatures get a speed bonus above 50% health.
Dark Phoenix Hatchling.
Gilnean Raven. (Start a Worgen character, it's the racial pet).
Lil' XT. (Common TCG pet. You can often buy the card on eBay for $5) This + a Howl pet will destroy many Legendaries, including Lil' Oondasta.
And, as Abbotta said, Mr. Bigglesworth. Very good for several tough battles, especial the King & Queen Floret in Garrison.
With Children's Week on now, you should probably get Legs and a Curious Wolvar Pup if you can. Both are good back-up in some Garrison and CT battles.