Which of your pets are you most looking forward to upgrading to rare? Since I don't expect the battle stones to be very common or cheap, I'm making a list of my priorities for each family, and I'm curious what other people are planning. Do you want to upgrade that poor Minfernal or Scourged Whelpling? Or would you rather upgrade one of the pre-MoP pets with an interesting moveset that you've been neglecting due to its Uncommonness?
Undead: this is my top priority overall -- Ghostly Skull. He has two nasty burst damage abilities and can self-heal with Death Coil, or he can choose Unholy Ascension
, which is unique to him and provides a ton of extra damage for your later pets. My only hesitation is that he has 3 breedIDs, and I'm not sure which I like best. I also have a rare Scourged Whelpling already, which made this choice a bit easier.
Magic: no, not Minfernal! -- even though mine is poor. I'm leaning toward Enchanted Broom, since he's incredible against Aquatics and has a neat unique ability in Sweep
Mechanical: so many choices, due to all the old Engineering pets: I'll probably choose Mechanical Pandaren Dragonling, since he's great against Magic pets and is similar to Darkmoon Zeppelin, which I like a lot.
Humanoid: probably Winter's Little Helper, due to a potentially vicious moveset of Call Blizzard, Ice Lance, and Gift of Winter's Veil
. I'd much rather not use battle stones on wild pets, but I might break down and upgrade a Flayer Youngling with the right breedID, since there's 10 breeds and finding a rare of the one I want is a bit daunting.