oohhh good thread / question!
Its a very close one, the sound on megadrive was always better IMO. But the graphics was better on SNES. Also the variety of games was slighty better for SNES
Close one -
SNES - Steet fighter 2 Turbo, FZero, Mario, Mario Kart, Donkey Kong, Killer instinct
Megadrive - Street of rage, Golden Axe, Altered beast
I'm going to say SNES, purely because I loved Mario Kart and even bought a snes a few years ago when at uni. We had a big Mario Kart tournament
Mario Kart on all other consoles is still not as good as the original