The swarm is a great kill streak. I'm going to give a small bit of advice about how to actually make the swarm better. Call in dogs and the swarm at the same time. The thing about the swarm is that people never use the perk to hide from it. I know I don't have it equipped on any of my loadouts. Neither do very many other people either. The problem is though that when someone does get a swarm you just simply go inside. Problem solved. However you then throw dogs in the mix and yea dogs may only get you 1 or 2 kills but they are simply there to get people spawning outside or running from them which in turn leads them into a swarm.
My stats with all of the streaks back this up. I average around 8 kills per swarm which may not seem like much but you then throw in on average 4 kills by dogs plus the fact you can still fun around and net maybe 4 or 5 more kills give or take makes the swarm a very deadly killstreak.
The one argument that I can agree is better about the lower streaks like the lightning strike or what not is that you will get more of them during the course of a game so while you get less kills per strike on average you get more of them. Other then that the swarm is a great streak.