Having played a game (Air Warrior) that had a different system in place to deal with team killing, I prefer AH's method.
In AH, you're only penalized once for shooting someone else on your side. In AW the penalty could last for 24 hours and depending on how many you TK, the penalty (PNG - Persona Non Grata) could last up to a few weeks. Now imagine not being able to fly a fighter for 24 hours or longer with AW's system.
Forgot how WB handled it.