For PvP I would definitely recommend a cat with a fast attack speed, like Broken Tooth at 1,0. This is very strong against casters since it will interrupt their casts a lot, and cats also have higher dps than wolves. If you're still BM specced, a good kitty will destroy mages :^)
In dungeons it would probably depend on your group. If there are 2 melee dps for example, furious howl would probably be more helpful than having a cat purely for your own damage output. If not, a cat might bring more overall damage to the group. I use a wolf for everything except PvP, but it probably doesn't make a huge difference in most dungeons.
In raids however, you should definitely go with a wolf over cat. If your raid leader is setting up groups correctly, you should have at least 3, maybe 4 melee dps in your group which makes furious howl very useful (along with Trueshot Aura). And in fights where your wolf would die instantly to the boss, you can just keep it next to you and use furious howl to boost your own damage (macro multishot + furious howl since they have the same cooldown).
I hope this answers your questions