The P-51 only ever came into it's own when it was fitted with a British Merlin engine. After that it was spectacular.
I'd vote for the Spitfire as the most consequential aircraft of WW2. At the moment of Germany's greatest strength this aircraft saved England and handed the Germans their first major defeat. This aircraft was the one that carried the day at the exact moment when all could be lost and England faced it's greatest peril.
In the Pacific once the F6F Hellcat showed up the Japanese were lambs to the slaughter. It's predecessor the F4F Wildcat had a 1,300 HP engine and was easy pickings for the Zero the first two years of the war in the Pacific. The Hellcat had a 2,000 horsepower engine and immediately upon deployment on US carriers began sweeping the skies of Zeros and everything else the Japanese had.
The P-51B and up only had about a year in the ETO and even less time in PTO. While it did save some Allied pilots lives just by being there it actually made very little difference to the war effort. The war would not have ended up being any longer without it.
During the Battle of Guadalcanal Campaign the P-39s were often bailed out by a F4F screaming in. The F4F got plenty of it's own licks in and there were worse birds out there like the P-39.
And if you look at the number of Luftwaffe Fighters during the BoB, you would see that not only the bulk of the bombers were shot down by the Hurricane but more than half the fighters. As I heard another person say from the Avionics world, during the BoB, the Spitfire was still under development but the Hurricane was a mature weapons system. When the upgraded the Spit, they just cycled the number up. When they finally got the Hurricane upgraded, it was called two different other names; Tempest and Typhoon.
