Concerning the Earthworm Jim games, I would give the edge to the Mega Drive/Genesis both times. I believe the game was designed with Sega hardware in mind, so it makes sense that it'd be best represented on that console. The Super Nintendo can push more colors on screen at once, and has a more versatile sound chip with multi-channel sampling. Despite this, I still believe the Sega versions are superior.
I have to agree, the MD/Genesis version looks slightly better than the SNES version.. could that be the video quality though??? Eitherway its a close run thing. I have to say the Gameboy version looks pretty good also.