Is it a mech stone? If so then most people wait to use them on pets that can't be farmed until you get a rare in the wild... like a Mechanical Pandaren Dragonling.
I tend to use them on pets I like to battle trainers with that are very rare spawns, like Scourge Whelpling or Minfernal. If I don't have a hard to catch spawn that I prefer to battle with then I use it on non-wild pets that only come in uncommon. I personally do not consider the Fluxfire Feline or the Cogblade Raptor to be hard to farm.
If it is a non-specific stone then I'd throw that sucker on the AH for lots and lots of gold.