No comparison you can't compare mario games with sonic games. Mario wins easily.
As far as the whole library goes pretty comparable as far as quaility goes, the snes and the genesis console.
Sonic games are way to over rated, there are plenty of games wich are way better on the genesis console. Sonic is a nice mascot with some decent games nothing more nothing less.
I have also read that some games were better on the snes pretty false in my opinion.
Hyperstone Heist vs. Turtles in Time - SNES
Castlevania IV Vs. Bloodlines -
SNES Genesis
Contra III Vs. Hard Corps -
SNES Genesis
I'll give the win for turtles in time to snes but the other two titles are definitely allot better on the sega console.
As far as music goes Sega did a way better job pretty unique espcially with sega titles such as michael jackson's moon walker, I cannot imagine that game with an snes sountrack would suck pretty bad.
Also some game had really nice and sharp grapics wich the nintendo consoles do not have not to mention It's processing power was higher.
More charaters on screen than on the snes console for certain games since the snes could not handle it.
As far as grapics go I don't know of any snes games wich such great detailed 2D grapics as shinobi III
https://www.youtube.com/watch?v=uNGbAStPXZcSome come close such as mega man x series etc but not as clean as shinobi III
The only reason why most people find the Snes better is because most people only collect or play snes and don't give the sega consoles any chance at all. Allot of poeple don't look at the games and think It's a system with only sonic and sports games. ofcourse such people bring hype to the nintendo consoles while the sega consoles are left in the dust since people do not recommend it. Still though far to many collectors for sega stuff but not as hyped as nintendo.
Also as far as mascots go, Nintendo had memorable mascots aside mario that's also one of the main reasons why people remember such games because of the popular franchises with their main charaters
As far as other games go snes gems of unknown series are also not remembered very well.
If you like arcade games Sega is King no questions asked.
For the best Rpg's and normal games Nintendo is your man.