For worst bomber, the Mitsubishi G4M "Betty" wins hands down. A huge, lumbering target, with vulnerable, easily-ignited fuel tanks, the Allied fliers who downed this turkey in droves didn't call it "the flying Zippo" for nothing. The unfortunate Japanese aviators assigned to serve in it did so unenthusiastically, as I understand; they were aware of its shortcomings, and that each mission was likely to be a death sentence. I have a hard time thinking of any WW2 combat plane, built by any combatant nation on either side, that I'd feel more trepidition about having to fly in, and that includes even the biplanes, and the Luftwaffe's 1945 desperate gambles, some of which didn't even look like airplanes, that were sent into battle as soon as pilots crazy enough to fly them could be found. The G4M Betty tops them all.
After Nagasaki, a Japanese surrender delegation flew a pair of these to meet the Allied commanders. I guess at that point, they no longer cared if they lived or died. Later, captured Betties were flown by the French and Indonesians in the conflicts which followed the Japanese surrender. They must have been terribly desperate, and willing to take anything that would fly.