This is one of those questions that has no answer! The fact that one pilot over another has so many variables that it would almost make impossible if not impossible to state single individual as being the best. There are so many variables, like mentioned before, theater of war, aircraft flown against, particular enemies pilot training and on and on.

When I meet anyone who has flown combat, I just have to admire them for their bravery and skills as a pilot, no matter if they shot down someone or got shot down themselves. As a pilot, there's certain amount skill you need, as fighter pilot there's a skill set that goes way beyond the average person, as a fighter pilot in combat, there's a a realm that those who haven't experienced it, can never really grasp.