Rick is right about sticking up for the system you own, but the Genesis might be my favorite system of all time. To be clear, I also like the SNES, and I agree SMW is better than Sonic 1 (Sonic 3 gives it a run for it's money). And games like Sim City and Super Metroid are great and aren't on the Genny.
But let me highlight some of the advantages of the Genesis over the SNES (and yes the SNES has advantages over the Genesis in other areas).
Genesis did it first - The Genesis came out TWO YEARS before the SNES. In that time it was able to already build up a nice library and 3rd party support from the likes of EA. It may not matter today, but it's still amazing that despite not having the most up to date technology, the Genesis went toe to toe with the SNES.
Expandability - I owned both the Sega CD and Power Base Converter and really enjoyed being able to play both last-gen and next-gen games on my Genesis.
The Controller - I will fight anyone about this one (not really). The Sega Genesis 6 button controller is better than the SNES controller, especially with fighting games.
The Look - I simply prefer the sleek black Genesis look of the blocky gray SNES look.
Blast Processing - Blast processing is real. The Genesis ran faster than the SNES. This made games like Sonic work, but where it really shined for me, was the sport games. The Madden & NHL series are two of my favorite of all times, and they played silky smooth on the Genesis. Their SNES counterparts, not so much.
Better Games Than The SNES Counterparts - Of course this is subjective, but Aladdin, Batman & Robin, Jurassic Park, Captain America and Mickey Mouse Illusion games are typically regarded as better on the Genesis, and in general, so are sport games and shooters.
The Exclusives - This works both ways, but series like Sonic, Streets of Rage, Shinobi, Phantasy Star, and Toe Jam & Earl were only on the Genesis. Wonder Boy & Space Harrier had fun Genesis installments and the Oasis series got it's start here. Ghostbusters, Moonwalker, Quackshot, Comix Zone and Gunstar Heroes are some other Genesis exclusive worth playing.
In the end, both the SNES and Genesis are great systems with some great games. Want to play Super Metroid? Play the SNES. Want to play Revenge of Shinobi, Genesis Does. Want to play an RPG? SNES is probably best. Want to play a shooter or sport title, go with Genesis.