My general rule of thumb in a multi-on-multi engagement is, if I have the opportunity to put down an enemy aircraft without sacrificing too much position, I take it. That which is dead cannot harm us anymore.
Too often I see 4 or 5 friendlies ghanking a single opponent down to the deck while I watch on radar as additional enemies are approaching.
And that's just the nature of the beast. I do the same thing, if I see a bunch piled on a bandit on the deck, I try to get into position for the inevitable high bandit(s) coming in to start BnZing them. It always brings a smile to my face when I see a pony dump 10k of alt to attack friendlies on the deck while I set up on his high six for the inevitable zoom.
When I'm in a crowd and there's an opposing crowd, my first priority is to get high, then work the enemy from the top down, either killing them or pushing them down to within range of the people who consider 6k alt to be 'high'. I prioritize buffs if I see them, but if I don't then I start working on fighters.
Wiley.