I know a LOT of people who cannot discern the differences between an F4F Wildcat and the F6F Hellcat, though we can all tell easily enough simply by where the wings join the fuselage. There are little things, but important, too. Most folks are NOT really too informed on such things. I am not one of "you knowledgeable folk" but I'm here a lot, and I read a lot of what you write.
If I had a guess, the most popular would be, in no particular order, Mustang, Spitfire, B-17, Bf-109, C-47s, and probably the Zero.
That takes care of the major combatants, and most of these choices were used by their allies, too. I'm ignoring the minor combatants, because the French and Italians were, as noted earlier, weren't in the war that long.
I picked the Mustang as " most important" because if it couldn't get there, it couldn't fight. The range of the P-47 limits it a lot. The P-38 had a lot of issues, too, superchargers blowing up, freezing pilots at higher altitudes, easy to spot and identify, etc.