I find Windserpent to be more effective than cats in the overall.  The windserpent breathe lightning usually does over 1.5* it's tooltip damage in the combat log, or more.  Due to the Nature resistance in PvP being low usually, the enemy will not avoid it, and does great damage.  However the pet still *IS* flawed in that when casting lightning your pet will stand still often.  Even with swoop 3 this is a bad loss of speed.  If you try controlling the pet yourself you will find that you can cast it while the pet is moving.  Cats have their purposes but I don't think they are the End-All pet.  STOP GETTING CATS AND DIVERSIFY DAMMIT.  Wolves, Wind Serpents, Bears, Wolves, Bats, and the others even have their strengths.  However, Bats + Rocs / Wind Serpents are the best in PvP, the Bats will kill your enemy's power (sadly with less personal gain) and the Wind Serpent lightning will kill your enemy at range when it must be done.

Don't be a pet fanboy (as in, OMG CATS FTW).