While the stones are a great way to upgrade pets, I would be careful what you use them on. The stones are fairly rare. I do all of the dailies that result in the sacks every day and I get maybe one every other day. Sometimes I go a few days without getting any and then one day I will get two.Wild pets:
For most of these just hunt them over and over till you get a rare. This may not be easy for some pets like Minfernal
and Scourged Whelpling
both of these I didn't hesitate to use a stone on since it was not easy to find these up, let alone farm for rares.Rest of the pets:
Many pets come in only uncommon variety, one example is Sea Pony
, these are the pets that most are using the stones for.