depends on the scenario, if im defending a base, and a damage a target enough that he is no longer a real threat, or easy pickins for somebody else, ill favor retaining me "E" over getting the kill. But if im out hunting, i'll glue myself to a target as long as I can, until his buddies come to save him, or one of us is dead. (and BTW, it's who ever did the most damage tha gets the kill, if you shoot him to pieces and he's still flying, then I come along and get a pilot kill, I get the kill, you get the assist)