It might not be too big a surprise that Cats are far and away the most popular pet at a count of around 9500, nearly doubling again the amount of Wolves, who come in just under 5000, which are in turn used in numbers over twice as much as the next popular choice, Gorillas, who are just above 2800 in number. Now mind you, this information does take into account pets that are in the stables as well, and there's certainly the possibility that a lot of them have just stayed in the stables for a long time.
Still, it's sort of crazy to see a handful of pets blow away all comers. If Cats and Wolves seem to insurmountably blow them all away, is it is a sign of overpoweredness, or just a sign that no matter what new skins and pet families you implement, people will always return to their old favorites? Or does it just mean that a bunch of old Hunters used Cats and Wolves back when they were one of a handful of pets available and just stuck them in a stable for old times sake rather than abandon them? One also wonders how Scorpids and Ravagers got so unpopular so fast. They used to dominate in Burning Crusade. Are we so fickle as Hunters that we just wanted to abandon their ugly faces as soon as we didn't need them?
Then there's the other question: Do the poor pet types at the bottom of the barrel deserve buffs, or are they a lost cause? Does Blizzard even care much about pet "skin" balancing, or do they just assume that no-one loves those ugly Sporebats? We do know they care about pet appearance to some degree, though, thanks to the Worgen debacle and the older slime debacle and the even older Ghost Wolf debacle.
Speaking of Slimes (and Hydras), Zardoz's data on the percentage of pets also includes a listing of what specific pet mobs are the most tamed for each family. For Crocolisks, it looks like far and away it's the now hot fixed to be untameable Hydra and Slime from the quest A Cleansing Song. Again, a lot of these "Crocolisks" are probably hidden away in stables now, but it at least suggests that people like awesome pet looks. You can see this in action with Boars as well, with the Rotting Ama'gar holding a commanding lead over all other comers, and even with the very popular wolves, where the demonic-looking Vargul Blighthound leads the pack.
Of course, other pet types, such as Hyenas and Cats, you'll actually find that the most popular pet mobs are the most high leveled ones. You'd think this would be less of a problem in the modern WoW game, since your pets automatically level to within 5 levels of you anyway when you first tame them, but it seems like people still like to take every slight advantage they can get.
One more interesting thing Zardoz points out is that just under half the pets in his sample have no spent talent points. Now, again, it could be these are just old pets in the stable that haven't been pulled out and talented ever, but there's also that whole weird thing where pets seem to lose their talents when their Hunter switches specs and all that gets a bit annoying. Maybe this kind of statistic will convince Blizzard they need to check into hammering out that pet spec switching stuff, though.
It's probably not completely safe to say too much about this data. It's pretty raw, and doesn't cover frequency of use or style of play for each pet, so we don't want to jump to conclusions too quickly, but at the least it should be fun to check it out and see how popular (or unique) your favorite pet really is.