Pound for pound, the Genesis has just as many gems on it as the SNES, maybe more. And if we're bringing up the Sega CD and 32X, there are even more excellent games you could throw in Sega's corner. Hardly a sucky consoles when compared to any console imo.
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Imagine the laugh in your head, because you can't embed videos.
You know the laugh.
Pound for pound the Genesis vs. the SNES is like putting a featherweight boxer against a LITERALLY GODZILLA. The SNES is overflowing with ultra classics that are still referenced as comparisons today, while the Genesis is mostly known for that one hedgehog guy who's terrible now. This is for two reasons: Nintendo's legendary first party games, and the fact that SNES had all the RPGs.
Nintendo's first party line up is so full of heavy hitters that it alone knocks out the Genesis library. Super Mario World, Yoshi's Island, Super Metroid, Donkey Kong Country 1-3, Super Mario Kart, Super Mario RPG, Earthbound, Kirby's Super Star, Starfox, Legend of Zelda: Link to the Past. This isn't even mentioning things that where more or less first party at the time, like the Megaman X Games.
When it comes to RPGs... do you hear people talking about Phantasy Star III being one of the best of all time... or Final Fantasy III (IV)? There is nothing wrong with the Phantasy Star games, I enjoy them, but TALK about being overshadowed both in terms of popularity and quality. Final Fantasy II & III, Chrono Trigger, Breath of Fire I & II, Lufia II, Secret of Mana, all huge hitters. It also had many more lesser or niche RPGs (Soul Blazer Series, Secret of Evermore, Lufia & the Fortress of Doom, Ogre Battle, etc.) which alone made up 5x the library of Genesis' total RPG library.
Individual gems... of boy. Again, the Genesis is buried in a landslide of SNES greatness. ActRaiser 1 & 2, Demon's Crest, E.V.O., Harvest Moon, etc... countless others. Now, what is qualified as a gem is hard to define, but the variety was just so much higher on SNES.
Another big category where SNES pretty much dominates is similar or shared games:
Hyperstone Heist vs. Turtles in Time - SNES
Castlevania IV Vs. Bloodlines - SNES
Contra III Vs. Hard Corps - SNES
Furthmore, in most cases where a game multi-platform it was usually better on the SNES.
With Fighting games although Genesis got the head start by not censoring blood, when the SNES followed suit it was the superior Mortal Kombat & Street Fighter system because of it's controller design.
Compared to the SNES... I honestly have a hard time writing up too much about the Genesis.
It's ultra classics are only a handful, and I am a bit reluctant to call them as such because a lot feel more like gems rather than things people remember from the time. Consider this a list of the best Genesis classics & gems combined because Sonic is 95% of what people remember: Sonic 1, 2, 3 & Knuckles, Gunstar Heroes, Rocket Knight Adventures, Shining Force 1 & 2, ToeJam & Earl, Earthworm Jim 1 & 2, Phantasy Star II-IV, Verctorman 1 & 2, Sparkster, Ristar, Comix Zone.
Some extra thoughts:
I think they are about equal, but Genesis Aladdin is usually considered better, an extra point I'd give to Genesis
Earthworm Jim 1 & 2 is better on Genesis as it was where it was originally intended to be
Sparkster on both consoles where great so I don't wanna give either console an edge on their unique versions
Some Shoot 'em ups where better on Genesis with more levels, as was Lost Vikings, though only SNES got the second one.
Both systems had a ton of mediocre to pretty good random platformers, but I feel SNES vastly overshadows Genesis in quality and uniqueness overall
32X & Sega CD... you 4 reelz, son? That adds about 3.5 good games.
In the end, opinion is opinion, and liking the Genesis more is just fine. However, I am trying to judge them on a level of public opinion and overall importance. Everytime someone is writing a top 100 games ever list you have a dozen SNES games butting heads for spots in the top 10, often filling at least 3-4 spots, where as you might have Sonic 2 or Gunstar Heroes somewhere in the 50s to 30s. On top of having so many games, the SNES was just in most ways a superior system in terms of hardware and capability, which led it's games to be much more daring and take much greater technological leaps. We individuals of the era will always be Mario and Sonic trying to one up each other, coming full circle to the point of this thread, but in the eyes of history, Mario and his SNES seems to have crushingly won. This doesn't make the Genesis not a great console, it has it's own flavor and unique software that make it worth owning alongside the SNES. However, I find it hard to argue from a rational position the Genesis changed gaming the same way the SNES & it's library did.
TL;DR
"Nu uh, SNES is totally better then Genesis!"