I've recently switched to a wolf for leveling with (one of the demon puppies from Zul'drak), and I'm loving it. He has tons of skills to stay alive, does a fair amount of damage, and holds threat just fine with Aspect of the Beast. I'll probably stick with him up to 80, then level up my wind serpent...at which point I get to decide which family I want to raid with, and that's going to be tough.
Ferocity does great damage and has a lot of skills to stay alive and happy--it doesn't matter that my wolf only eats meat, because I never have to feed him. Cunning seems to do a fair amount of damage, too, and the more points I can spend in the tree the better it gets, even if most of the damage skills are fairly situational. The big thing I'm looking at is Roar of Recovery, though. It's a long cooldown, sure, but in the past it's meant the difference between switching to viper on boss fights, or going all out for a bit longer. It seems almost too good to give up by switching to a Ferocity pet, especially since I like to save my potion for a healing potion just in case. On the other hand, lightning breath really doesn't do a lot of damage anymore, and I've been getting frustrated with my wind serpent's lower DPS even if the extra mana keeps me going longer.
I'm leaning towards my wolf for soloing (especially if his howl doesn't stack with trueshot aura, as we usually have at least one marks hunter in the raid), and my wind serpent for raiding just for the mana return...I'm not sure though, I'll have to pick up some cheap arrows and experiment a bit. (Of course, if I hit 80 before they fix the hydra, I might just bring a tenacity pet along for pure awesome. Crossing my fingers on that one!)
Which pet families are you guys planning on using for raiding?