The Commodore SID is a waveform synthesizer. The SNES sound chip is a sampler. They are two different classes of synthesizers. The SNES sound chip has the opportunity to sound much more realistic given good samples. But this doesn't mean it is "better" in any way than SID - they are incomparable because they are fundamentally different. For example, what if I don't like sounds that sound like real instruments? Listen to some of the C64 compositions. Would they all have sounded better with real instruments?
Now if you were really cool, you could create a SID instrument, sample it, and play it on the SNES chip. Hmm.