Depends really. Leveling should try to find a balance in there, with more HP than armor. Because while you are soloing your pet will be taking some damage and armor is good to mitigate, but of course HP is more important to survive things that armor doesnt mitigate, like magical spells.
Once you hit 7 and begin heroics and raids. HP is your number 2 priority. Number 1 priority is your offensive abilities, after all your pet basically is an overgrown dot.
You want to max out your stamina talents next to be able to survive those volley spells and ramdom casts, from some bosses.
Armor is less important because, once in heroics and raids if your pet gets targeted and hit, even with full natural armor talents will only survive 2 or 3 hits from a mob.