As much as I love Sonic the Hedgehog, Super Mario World is miles ahead. Both where important to me, and I think they may have been the first 2 games I ever played (My daycare center had them when I was 5 or 6). Super Mario World just had a lot more to do, more variety, a more complex method of playing the game (all the secret levels and whatnot) and when I finally got my first system it was SNES over Genesis in no small part thanks to Super Mario World being the better game (I had beaten Sonic at the daycare, but never had enough time to find everything in SMW).
All three Genesis Sonic games probably can't compete with just SMW, but Sonic 2 has one of my all-time favorite soundtracks so it has that going for it.