Both systems have amazing games and killer exclusives, but for me the Genesis wins. Usually the darker pallet of the Genny was better suited for conveying atmosphere in games. Music is also VERY important to me and the FM synth chip in the Genesis is generally more apealing to me.
Don't get me wrong. The Genesis has no substitute for Snes musical masterpieces like Final Fantasy 6, but usually the organic nature of the Genesis's sound and graphics is more unique and refreshing to me than what the Snes has to offer.