I voted for the Beau as it was one of my favorite 2 engine planes in old IL2 but Do17 is closely behind as it is a very beautiful plane.

The Defiant is a priori a must have for early stages of aerial warfare scenarios on Western front but I fear few players will fly it because as pilot it is only piloting no shooting or as gunner - well, you're just a gunner ... so only those liking to be gunner will actually fly it I think.