I have to go with Super Mario World by a huge margin. I just played through Sonic 1 again, and it's barely even above average. The levels have a lot of complexity, but there are many problems where enemies and hazards are nearly impossible to avoid because you literally cannot see them without pausing to look up or down. There's way too much "waiting" necessary, and the level designs don't seem to have been created with Sonic's speed in mind. It almost feels as though the game was a very ordinary platformer which had Sonic shoehorned in at the last moment. That said, the music is fantastic.

Lest anyone think I'm a Sonic hater, I absolutely love Sonic 2, Sonic 3, and Sonic and Knuckles. Those might actually tempt me to go against Mario.