Although the P-38 Lightning is my favorite, I had to vote for the P-51 Mustang,
A glaring omission is the Hawker Hurricane which although slower than its contemporaries changed the face of history.The Hurricanes brought down two thirds of all enemy aircraft during the Battle of Britain.There were nearly as many built (14 000) as the P51 Mustang .
Although the P-38 Lightning is my favorite, I had to vote for the P-51 Mustang, simply because of what it did for long range bomber escort. I Would have voted for the Spitfire, due to it's success over England, during "the Battle of Briton", but I felt that the long range escort aspect edged it out. Plus, it's speed and maneuverability were an asset in dog fighting, and towards the end, when Germany finally developed jet fighters.
Very good point and lets not forget about the Wildcat
Hm, it's not exactly my field of expertise, but counting out the new technological innovations of 1944/45 (turbojet- or rocket-powered fighters like the Messerschmidt ME 262), I'd say the Mitsubishi A6M Zero was a pretty dangerous and effective fighter plane. If the Japanese would have had the same amount of "human resources" and material as the US, the Pacific war would have been very different, as the Zero was faster than almost every other fighter plane and the pilot training of the Japanese was superior. But the reality turned out to be different.
If bombers of any kind weren't excluded (even the smaller ones and the dive-bombers), I'd probably choose the Junkers Ju 87 Stuka. By the end of the war it was outdated, as the "age of the dive-bombers" only lasted from about 1930 to 1945, but when it comes to the "greatest" plane of WWII besides the Superfortress and the Zero, I'd choose the Stuka. It was used as a dive-bomber, ground-attack aircraft and tank hunter. With it's countless merciless attacks in the first two years of the war especially against Poland and France it became the symbol of the Blitzkrieg. The effectiveness and relentlessness of these machines was legendary. The fight logs of the Luftwaffe show, that just one of the Ju 87G of the famous Rudel-unit destroyed 519 allied tanks and armored tracked vehicles. The Stuka's trademark, the "Jericho-Trompete" (the "Jericho Trumpet", a kind of air-propeller attached to the plane's hull making a siren-like sound), became a source and symbol of sheer terror. The Stuka was Germany's WWII-version of shock and awe, so to speak. I read a lot of eyewitness accounts from people who survived Stuka attacks and it seems that it must have been horrible. I recall, there was one very sweet old lady from the Netherlands who still today wets herself if she hears a sound resembling that of a Jericho-Trompete. I cannot imagine the horror these poor people must have lived through. The grandfather of my fiancée flew Stuka a couple of times before he started flying fighter planes. According to him, these things were pure death machines.
A case can be made for the P-38. This plane shot down more enemy aircraft than any other fighter in the Pacific theater. An awesome plane with tremendous range and loaded with fire-power....and so cool-looking with the twin-booms.
http://www.ww2incolor.com/gallery/albums/new_war_photos/p38lightning_water.sized.jpg
There's another first class aircraft called the de Havilland Mosquito which began life as a fast bomber (at the time it was actually the fastest aircraft in the world) but some of them were used as fighters and were particularly effective at night.
It was probably the best overall aircraft of the war , it could carry a 4000 lb bomb (which the B17 couldn't) yet outrun most enemy fighters.
There's another first class aircraft called the de Havilland Mosquito which began life as a fast bomber (at the time it was actually the fastest aircraft in the world) but some of them were used as fighters and were particularly effective at night.
It was probably the best overall aircraft of the war , it could carry a 4000 lb bomb (which the B17 couldn't) yet outrun most enemy fighters.
My grandfather was in the RCAF 410 Squadron, I've got a great shot of his squadron all lined up in front of a mossie at the end of the war. He left me even his training manuals and so many pictures as one of the groundcrew - he loaded the 20mm Hispano cannons and fit the various bombs. My molst prized pics are of a prisoner-of-war facility they bombed with precision to enable POWs to escape
The Mosquito was made of of mostly laminated plywood, and fast as fuck.
Still, my fave is the P-47 with it's eight .50 and rocket capability. I love them tank busters