The highest scoring pilot was likely to have been the one that either never got shot down or survived getting shot down.
Key Performance Indicators
1 Number of Missions Flown.
2 Number of Wingmen lost (In his 1300 missions Hartmann is proudest of the fact he never lost a wing man)
3 Number of times shot down (Hartmann was never shot down, his plane got damaged by debris though one American chased him down till he ran out of fuel but graciously didn't shoot his parachute which often happened.
4 Ratio of Victories / Number of times shot down
5 Total number of times shot down.
6 Total number of victories.
Of course getting shot down over your own territory while attacking a B17 is a different matter to getting shutdown by another fighter. When protecting your own people over your own territory you are supposed to and able to take a greater risk than when over enemy territory.