SNES is better. 
In terms of audio/sound quality? Sure, they had a Sony made chip (partially?) due to the potential impending partnership for a CD-ROM add on which we all know the end result of. BUT the Genny's FM Synthesis chip has a special buzzy/farty sound to it that when made use of well results in some amazing stuff with a classic arcade-y sound. I was a SNES brat but knew a person or two with the Genesis and thus mostly missed out on it, threads like these are a treasure trove of sonic ambrosia for some of us. The SNES gave people a larger pallette to work from sonically and it's impossible to argue with the work Kondo, Mitsuda, Uematsu et al did on the machine, however some peeps mastered the limitations of the Genesis and produced some incredible work within those confines. It's like asking do you prefer Jack White's work in the Stripes or his other/solo material that's more blown out. One doesn't invalidate the other, maan.

I cannot and will not try to argue against THIS:
That 16th note bassline with a fucking trumpet lead and those panning harps, cot dam.

But that Batman piece I linked earlier is also absolutely godly.