Optical or coax?

Assuming that equal quality cables are used which provides the best SQ when connecting a streamer to a DAC?
I always heard ever since the very beginning optical was not as good as coax. Who knows why? Theoretically optical should be light years ahead.  
Generally speaking Coax is the way to go for audio because it's a simpler transfer of information.

As I understand it optical takes an electrical signal and converts it to light and then back to an electrical signal so there is more of a chance of losing information in that process.

At the end of the day both will pass signal and some devices such as the Sonos connect are said to play better from their optical output.

I would just get myself a decent piece of 75ohm coax cable and be done with it - definitely nothing to lose any sleep over...
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