WITHOUT question the MG42.
try killing B-17's with 50's without getting killed
I use 50s to kill bombers almost exclusively. I save the canon for the harder planes.
That cause the plane you fly only has one cannon. What's harder than taking down a B-17?
A well armored fighter like a 190 or jug. Of the 150 rounds of canon I carry i often come home with over 100. I can put a stream of 50s into a plane with the 38.