Think outside the box and try to grasp what "the best" really means. It doesn't have to be the fastest, biggest, deadliest or even carry a bomb load, but look at how it contributed to the war effort, the effect it left on aviation history, how it compared to it's peers and finally its cost effectivness to operate. There is one clear winner here, the DC-3/ C-47.
Not so clear, take for instance the B29:
1. How did it effect the war effort: ended it with only 2 bombs
2. Effect on aviation history: Showed that an aircraft means that a major war cannot be won anymore.
3. Compared to it's peers? What active heavy bomber came anywhere close to this aircraft?
4. Cost effectiveness: 1 flight, 1 bomb, 1 city is the most cost effective way of ending a war (for the winner) that I can imagine.
Sorry Joe, couldn't resist