With the addition of the Mosquito B.Mk XVI we have the best British bomber of WWII. Even those who disagree with my assessment that the best British bomber was the Mosquito B.Mk XVI will almost certainly select the Lancaster Mk III as what they think the best British bomber was, and we have that too. We also have a candidate for both the best German bomber, Ar234B, and the best Japanese bomber, Ki-67, in the game as well. These are what I think are the most capable bombers, by nationality, of WWII are.
American:
B-29A Superfortress
Also ran:
A-26 Intruder
British:
Mosquito B.Mk XVI
Also ran:
Halifax B.Mk VI
Lancaster B.Mk III
German:
Ar234B
Also ran:
Ju188A
Do217E
*(I don't consider the He177 a contender due to its extremely poor reliability, though it may very well be wonderful in AH2)
Italian:
Cant Z.1007
Also ran:
SM.79-II
*(I don't consider the P.108 a contender simply because it saw such light service)
Japanese:
B7A2
Also ran:
H8K2
Ki-67
P1Y1
Russian:
Tu-2
Also ran:
Pe-8
*(the Pe-2 was clearly more important than the Tu-2, but it is also clearly inferior)