Pets will be differentiated less by species than by category: Cunning pets, Ferocious pets, and Tenacious pets. Each of the three categories has its own talent tree: Cunning, Ferocity, or Tenacity. It seems that Cunning is a utility tree, Ferocity a DPS tree, and Tenacity a tanking tree. Pets will each belong to one of these three categories. Additionally, each pet family (e.g., wolves, tallstriders, etc.) will have one unique ability available only to that family. For example, crabs have Pin, worms have Acid Spit.
I am not interested in Tenacious pets. But it's a hard call between Cunning and Ferocity. When I'm looking at a build, either for myself or my pet now, I have to consider both my own dps, and the buffs I can bring to a raid. It's nice if I can do the same damage as a ret paladin, but I don't exactly bring raid-wide utility to the table the way they do. Ferocious Inspiration only goes so far. So, what can my pet bring?
If I'm considering a Ferocious pet for pure dps, Furious Howl may be the best I can offer. The Cunning pet offers seem poor, but I can imagine a spore bat's Spore Cloud being useful for the armor reduction, especially since the effect would be raid-wide, not just applied to my party the way wolf buffs are. The bigger draw to Cunning pets comes from the mana problem I may have by running in Aspect of the Beast instead of Viper.
Say I take my wolf Cafall and make him my dps pet in Lich King. His build might look something like this. He'd have Furious Howl, Ferocious Inspiration, and Call of the Wild for my party. That's pretty good.
But let's consider a spore bat. We'll call him... Jularlmin, just because. Between Feeding Frenzy and Cornered, Jularlmin's build has the potential to deal more damage than Cafall would. And I pick up Roar of Recovery, a kind of hunter Innervate, which seems like a good way to address the issue of no longer running with Aspect of the Viper. This, in addition to the Spore Cloud ability.
In reality, I'm probably not going to have mana issues, any more than I do today. Since I won't be spamming Wing Clip anymore, the frequency with which I use mana-burning abilities will pale in comparison to a ranged hunter. And it's hard to argue that Jularlmin would be a better choice than Cafall in a raid setting. Although the Spore Cloud ability is a raid-wide effect, reducing the armor of a target by 700, I just don't think that's going to compare to the dps increase of buffing my party with Furious Howl and Call of the Wild. So while I'm using a ravager today, it looks like Cafall may be coming out of retirement in WotLK along with Gweryc himself.