Buzz Beurling is up there IMO. Maybe not the highest overall kills, but for the time he did fly and the theaters he was in, he racked up quite a score on the Allied side in short order. He was also considered one of the most aggressive and crazy fighter pilots of the war, added to having the reputation of being one of if not THE best shot in the sky on the Allies side.
He claimed a kill, and stated he fired exactly 5 20mm rounds into an Italian fighter, and the troops who found it found 5 holes in the cockpit. He also made several long range 800m deflection shots witnessed by others - he was known for his deflection shooting, as he worked on it tirelessly on the ground and in the air, and when his CO asked him to explain it and train him once, that CO the next flight after a few days instruction shot down 2 and got a damage as well, the very next flight.
27 Kills in Malta in 14 days, while sick with disease and down to 120lbs or less...He also shot down some of JG2's best 190 pilots in Europe in fights there for a total score of 32. His aggressive style got him shot down 4 times as well.
So, overall not a flashy high number, but as a ratio for "kills per time", he has to be one of the top few in the war for certain. He was a real nut too, his exploits on the ground are something hilarious to read about, but he was a dedicated student of primarily shooting accuracy, with flying ACM and tactics a close second, and studied them constantly to improve.
