I think all of those arguments have merit but they tend to be narrowed to give the crown to the plane a person already thinks is the best anyway.

The United States produced 276,000 aircraft in WWII. 23,ooo were lost in combat and a staggering 15,000 were lost in operational accidents, mostly in the US.  The loss rate from all causes was 13% of the total of all aircraft.  Remember this, it will factor in later on.

I think the best fighter of WWII argument is missing a very important and I think decisive argument that I will make here, but first the contenders for the title.

Curtis P-36 Hawk

Honorable mention as the first US-marked aircraft to bring down a Japanese fighter in WWII.  The Army built fewer than 300 Curtis P-36 Hawks but they hold an interesting place in history.  These were the first fighter planes to engage Japanese forces at Pearl Harbor on December 7th, 1941.  Popular movies have given this distinction to the P-40 Warhawk but it rightly belongs to the P-36.  This was their only combat action in the Pacific.  We did export a version of this aircraft to France which used them against the Luftwaffe when Germany invaded them in 1940.   They were actually quite good, the radial-engined Hawk fighter made aces out of 11 French pilots. When the US landed in North Africa in 1942, the French piloted Hawks shot down 7 US aircraft.