I'm not a basher, but optical makes use of light therefore can't be subject to electrical interference.
There's some interesting articles on a website for stereophiles that go into this in some depth, not to mention some papers on the Naim site too, if memory serves me well.
However, USB in theory should be as good if not better, though there are those who claim firewire is inherently a cut above both.
Personally, over long distances I prefer optical cables.