I would have to say the ball turret gunner. Atleast on the B-17. They were enclosed in this small ball and no where to hide. On top of that all that if the turrets electrical power failed they would be locked in there and then if the landing gear failed to lower they were really screwed if they were trapped in there. All that is hypothetically speaking but I would not like to have been in that turret. Not to say that other bomber crew members were not brave, they all were very brave aviators but you had to have a lot guts to climb into that ball turrett. Imagine enclosed in that glass turret with a Me-109G racing toward your with its armament blazing.