This question is as easy to answer for me now as it was in late 1991. I absolutely loved Mario and his adventures. I remember reading about the Super Nintendo and Super Mario World in Nintendo Power. I chose a Genesis over the Super Nintendo for reasons unknown (maybe it had not come out quite yet? I remember Sonic The Hedgehog recently came out and Altered Beast bundles were still available at Service Merchandise. I actually requested that bundle over the Sonic bundle.)
The Mario games always seemed like an subtle evolution over the previous games in the series. I finally beat Super Mario World 17 years after its release, but I had fun doing so. It has been 20 years since Sonic came out and I still can't beat the game. It isn't for lack of trying. The graphics are nice, the tunes are memorable, and the concept is not bad. I just don't have the patience to beat it. I think it has something to do with needing to get the emeralds to get a "good" ending. I detest any game that forces you to ultra-super-mega beat the game to beat it. I could have (and did the first time) beat Super Mario World with the shortest route possible without getting all the stars and I still won the game and got the ending I deserved.
I guess Mario's games are more rewarding...