Taking the best pieces from the worlds aircraft, what would the "Best" aircraft of the differing categories look like? Wings of a Ta 152, P-51 coolant system etc.
This reminds me of a song I learned as a kid. It was called "An Ordinary Dog", and the chorus went something like:
It looked like a part of a gorilla
It could be the descendant of a bear
You could tell it was related to a shaggy yak
By the length of its hair
Its legs were as long as any emu's
Its teeth were as sharp as any shark
A platypus's feet, and to make it quite complete...
The nose of an African aardvark.
The counter-question always has to be asked: FOR WHAT ROLE?
If I were the leader of a fictitious country that was going to take up arms on either side of World War 2 and I had to standardize on the fewest possible aircraft for front-line combat and further development, I would venture to suggest that on the Allied side, I would be doing well for myself if I chose the (Merlin) P-51, the Mosquito and the Liberator, and on the Axis side the FW-190, the Ju-88 and a four-engined He-177 (assuming I could get it built over official objections).
IIRC, several 'nice' US designs failed thus, did not go into production as could not grow to catch the 'goal-posts' that had moved during development --Faster ! Higher ! Longer range ! More guns !!-- or were designed too closely around an engine that simply failed to deliver...
Are we talking specifically about aircraft drafted between 1939 and 1945, or are we expanding the terms of reference to include the horrible experiences the US Navy had with the J40 and other such total failures?