Hmm... Naval Stewards aren't in the Army (per the title of this thread)... and Ninjas are part of CANSOFCOM, not the Army.
So I guess the toughest job in the Army must be the Army HQ G39: "Staff Officer - infliction of HQ's brilliant ideas prevention and mitigation". You know, the one person in the HQ who's supposed to keep stupid brilliant ideas from being inflicted on the rest of the Army.
I think that career managers have left that position unfilled for years...