Well its almost impossible to answer - or it depends a lot of what you are trying to do.
I like it a lot on Thunderift Falcons. From 0 armor and 5 life to 1 armor and 8 life. It make it a lot harder to kill.
But the point is not to get to attached to your pet and let your opponent kill it so that you can use Pet again.
It seem you will often lose 1 die when using Pet on the flyers, as they will often fight outside your zone.
Feral Bobcat is a creature i always loved, but never really got to work. Often it to will work outside the zone and thus so lose the extra +1 for fighting in your zone.
I like your idea of using it on a Guard Dog. You have to find a way of getting them to fight in the zone you want.
Change of Rage?, Thornlasher?, Mountain Ram?
I was thinking a long similar lines just before seeing your post when i was looking at Packleader´s Cowl.
And i was actually putting Ridgeback Skunk aside for something like that. But still some of the classic level 2 Pets Timber Wolf or Emerald Tegu seems good for something like this as well.
Theres a lot of higher level options as well. Almost all of them good.
If you wanna try a rage strategy its likely the way to go.
I don´t really do math, but i have a feeling that increasing low armor is a lot better than increasing high armor. That would depend on how much dice and piercing your opponent has naturally.
