The best place to punch differs depending on who the boxer is you are fighting. If the boxer is a heavy set boxer you may want to try to punch them in their face as it would cause more damage. If the boxer is skinny, you may try to punch them in their rib area.
The best place to punch is neck. It is because when you hit the neck, for few senonds person get unconcious and you get another chance to hit him whereever you want.
It really depends on your opponent, as certain fighters have certain weaknesses. However, the jaw is very vulnerable, as are the kidneys. These are the two most vulnerable parts of the body in boxing.
