If you are restricting the argument to which plane had the most contribution to winning the air war against Japan then is it the F6F Hellcat, no question.
It accounted for such a huge fraction of the total kills and its appearance is the point in which the paradigm shifted - the F4F held the line admirably and had victories, but the opinion was that these were achieved in-spit of the F4F not due to it. The appearance of the F6F gave a significant amount of confidence in the ability to win large air engagements and allowed a more daring carrier operations.
The F4U was a big hype that made very little difference. It started development was in service before the F6F, yet had almost zero impact on war progression, regardless of how many planes one squadron shot down - no carrier operations means it does not operate where it is really needed. Small production numbers means not enough impact.
P51s, P47s and P38 and even P-40 all had an important contribution, but being land based (like the F4U...) they were operating in the wrong (Ok lets say less than optimal) places. The Pacific campaign was all about naval war and the naval war was oddly fought in the air. You needed carrier planes for that.
The F6F is an excellent example of "less is more": development started long after the F4U and instead of trying to make the best possible fighter, Grumman made the most sensible fighter. The design was not revolutionary (most unique feature was the way the wings were folded) and stat for stat it is inferior to the F4U, but actually showing up to the fight is more important than hyping about a few mph and deg/sec roll rate. This was achieved by making a more reliable, easy to operate, easy to manufacture (breaking setting world production records) and to top it all, even cheaper fighter than the F4U. By the time Vought had finished tweaking their spoiled over-hyped child and produced enough to equip a couple of squadrons, the navy was already full of F6Fs actually wining the war. The F4U was the better plane, but the F6F was by far the more important plane.