To say which is best, you must first establish the criteria. Best in performance, most advanced, most significant contribution to aviation, most significant impact on the out come of a war, etc,etc.
That being said, I'm going to go with impact on war.
P-51 Mustang, it's performance and range allowed it to escort Bombers deep into enemy territory.
B-17 became the icon of American airpower being the first strategic bomber and it's ability to bring it's crew back.
F-4 Phantom was the backbone of the USAF and Navy during Vietnam and all the top scoring aces flew them.
B-52 the energizer bunny of the bomber world, keeps going and going and going
![Big Smile [:D]](/FSM/CS/emoticons/icon_smile_big.gif)
from Vietnam thru Armagedon.
Wright flyer, where it all started.