I know headshots are a critical if you're a sniper, or if you're a spy using the Ambassador, because it's labeled in the weapon description. I can probably assume it is the same for any other weapon, but are there separate modifiers for the legs, arms, torso, and chest?
For example, when I am playing Heavy and get caught in a close range ambush with another Heavy, should I aim for their head, or does it really matter?