From: Near Portland, OR
William Dunn who was one of the Eagle Squadron guys and later flew with the USAAF wrote a memoir and had a section in the back on what was the best Allied fighter. He said he's asked that question a lot. He said it all depends on your mission.
The Hurricane was rugged and reliable which made it well suited as a defensive fighter in rough conditions.
The Spitfire was a pleasure to fly. One of the easiest high performance fighters to fly hands down. It was an excellent point defense fighter, but had no range to speak of.
The P-38 with its twin engines was very well suited to long range missions over water. It's the only twin engine fighter that had any success as a pure day fighter.
The P-47 was decent in a dog fight, but it's rugged construction and heavy firepower made it one of the best ground attack fighters of the war.
The P-51 was a bear to fly. You had to be on top of it all the time. When fully loaded with fuel it was even tougher to fly. However, if you needed a long range fighter that could win a dog fight when it got there, there was nothing better than the P-51.
He didn't talk about Navy/Marine fighters, but the Hellcat and Corsair had their best missions too. The Hellcat was a superior carrier fighter because it had very good low speed characteristics which is a critical plus when doing carrier ops. It had 95% the performance of the Corsair so it was good enough against its foe. The Corsair was another thoroughbred fighter like the Mustang, but it was also a bear to fly like the Mustang. It excelled when flying from island bases, but even when they worked out most of the problems and put them back on carriers, they had a lot higher ops loss from landing accidents than with the Hellcat. At the end of the war the Navy figured it was worth it to have that extra 5% to get the Kamikazes.
He also didn't talk about the P-39 and P-40 which were really a generation older. The P-39 made a good strafer due to its 37mm cannon and the P-40 had the advantage of being available in large numbers when it was needed. The P-40 was never a top tier fighter compared to other modern fighters, but it was good enough and it was there. It also had a lot of the same advantages of the Hurricane, it was rugged and could be kept flying in primitive conditions which lent it to serve in far flung places where advanced repair facilities weren't common.
Though personally I like the look of the F6F. Especially in the three color camo the F6F-3s were painted in. It's not sleek, but it's not ugly either.
WitP AE - Test team lead, programmer