Does the attacking or defending player choose the order of wound allocation?>
Tough 3 model take a Laser cannon shot (deadly 3) and 2 assault rifle wounds. Does the attacker chose if he takes the laser cannon wounds first or the assault rifles? It matters whether or not the assault rifle wounds are tanked or go to the next model.
Whichever weapon was rolled first, is resolved first. The defending player chooses which model the wound(s) go on.
In other words you couldn't have fired a laser cannon and assault rifles at the same time, declare which one is first and then roll it.
So tactically, if shooting at a Tough(3), always fire and resolve your laser cannon first. If it kills that model, your upcoming assault rifle hits get assigned to another model in the unit (again, by the defending player).