I am not sure if my top choice would be the P-51 or the Hellcat. And of course near the end of the war jet fighter planes started to make an appearance.
The German ME-109 and the FW-190, and later the jet fighters they had were pretty good.
The British Spitfire was good; I don't know very much about the British Hurricane.
The Zero has to be somewhere near the top but I am not sure exactly where. At the start of the war in the Pacific the Zero was awesome. But later there were a few fighters that were pretty good against the Zero, such as the F4U, the Hellcat, the P-51, and the P-38.
I suppose you really have to separate the jet fighters that appeared late in WWII from the earlier fighters.
The P-47, and some other aircraft like the P-38, were very important in attacking ground targets.
In Europe the P-51 was very important because it was able to escort bombers all the way to their targets and back. So at least in Europe the P-51 would I guess have to be considered the most important non-jet fighter plane.
But the Hellcat was awesome in the Pacific.
Some of the fighter planes of WWII that do not impress me very much were the Buffalo fighter plane that was not much against Japanese Zeros and the P-40, although various versions of the P-40 were used successfully in China by the Flying Tigers. But they had awesome pilots in the Flying Tigers organization.
So I guess I would say the best non-jet fighter planes were the P-51 in Europe and the Hellcat in the Pacific.