For planes overall, the B-17, B-26, etc. are much tougher than fighters.
For planes that can dogfight, the A-20 seems to me to be the toughest, maybe followed by an Il-2.
Of planes that are specifically fighters, F6F's, F4U's, P-47's, F4F's, FM-2's, P-38's, and FW 190A's seem tough. Maybe Bf 110's as well -- not sure.
Mossies don't seem very tough in my limited experience of flying them.