Coax isn't always better than toslink. Like everything else, it depends on the application and implementation. If you're running a signal from a noisy source like a computer or cable box, toslink eliminates any electrical noise issues between the two components by isolating them electrically. My Apple TV 1 has optical instead of coax for this reason. I've tried coax and optical from my cable box, and optical was a good bit better. That's not an apples to apples comparison, as different coax cables sound different. But for the money, a cheap optical cable easily beat out a $200 or so coax cable. It wasn't the coax Cable's fault, IMO as its a great coax cable; rather, it was the implementation.
I have a Sonicwave glass toslink cable that was about $25 from Amazon. Sounds far better than several boutique brand plastic cables I've tried that were at least 4 times it's price.
At the end of the day, it all depends on the transport - noisy stuff usually does better with optical, and quiet stuff usually does better with coax. My Rega Apollo as a transport into my previous DAC sounded far better with coax than optical. Like the cable box, only in the opposite manner, it wasn't close.
All we can do is report our experiences. Your's may be different!