Depends on what we mean by programmer.

Fabrice is more clever and faster, I guess.

But John Carmack is in my mind a better software engineer. He writes elegant code that can be used and maintained for a long time. At least from Quake 2ish, but you can see signs of solid code architecture already in Doom.

Doom code will live almost as-is forever. The code Fabrice wrote for ffmpeg has been entirely replaced