Put them both on, kill shooter to stop the intentional friendly killings, but let the friendlies take the damage to to try and slow to morons from clearing your 12 oclock.
This does make some added excitement for sure.
In the game I currently play, I've had 3 enemy planes on my tail, one shot down his buddy trying to shoot me. The remaining two collide trying desperately for the kill and I laugh all the way back to my base with my shot-up plane.
The other one that's crazy with this is when you and a buddy are gong after the same enemy plane from different angles you need to be aware of where your teammate is so you don't collide and take yourself out of the fight.