Now the big question, what pets should I get for my army? Below are pets you should acquire, get to 25 AND make blue as quickly as possible. These will be your "go to" pets for many of the tamer battles.
Anubisath Idol. Can either be bought on the auction house or dropped from the Temple of Ahn'Qiraj. Save your gold and buy him from the AH as he is one that you will use frequently. Deflection always goes first and blocks ALL attacks during that round. His Sandstorm ability is awesome as will null or drastically reduce damage from skitter/stamped type attacks. Plus being Humanoid, will regain 5% of total health per attack.
Mechanical Pandaren Dragonling. Can be built be engineers with Pandaren Engineering or bought on the AH. Again, if you have the gold buy this one as will be used a lot. All mechanical pets can 'rebuild' themselves after death to 25% of their max health after death and unlike undead's they won't automatically die at the end of the next round.
Lil'Bling. Can sometimes be found in the Blingtron 4000/5000/6000 (not sure about the new 7000 model) gift packages. Can also be bought on the AH. This little guy can do some serious damage and can take a lot of abuse too. Can heal itself or cause damage with the Blingtron Gift Package ability.
Iron Starlette. Can be obtained by starting the Blasted Lands via Warning Orgrimmar (H) or Report to the King (A) at level 90 quest. Can also be purchase on the AH. This one can be really expensive, but is so worth it. This is a must have to easily beat Tamer Christoph VonFeasel at the Darkmoon Faire daily battle. Also comes in handy for a couple of the daily Garrison battles too.
Darkmoon Zeppelin and
Darkmoon Tonk. One of several purchasable (with prize tickets) Blue pets from Lhara on Darkmoon Island. Costs 90 prize tickets each and are the first two pets you should buy with your prize tickets and work on getting to level 25. Once you have more tickets, then you can buy, train and sell the other pets. Both are very useful against other tamers pets. A level 25 Darkmoon Tonk will make the battle with Jeremy Feasel (the other Darkmoon trainer) much easier. You will find you'll be using these two Darkmoon pets quite frequently against other tamers.