Is one group more deadly than the other? Or does it not make a difference? Right now there might be a lot of bias against a certain group so try not to let recent events prejudice your decision. Reasons would be appreciated. If you would like to mention your pick for least deadly then feel free to do so also.
My choice is religious heads of state. For my least deadly I choose the atheists since they are themost likely not to get into a battle over religion.