You've asked a question that has been hotly debated many times; perhaps the search engine is having issues since the forums were just re-arranged last week.
In any event, here is what you will find:
Group 1:
co-ax is better because of various deeply faithful reasons, people claim they can hear a difference. No real scientific proof. A belief, like a religion.
Group 2:
Digital is digital. 1's and 0's are just that - and an error in transmission is a flaw, thus cannot happen. Science.
Group 1 disputes Group 2, by claiming that optical is more susceptable to various corruption, and that all transmissions have errors, but coax have less
Group 2 will counter with: errors are unacceptable, and any hard-core geek Q/A tester would fail any cable that had ANY errors. Period.
Group 1 counters with "co-ax sounds warmer".
Group 2 replies: How can 1's and 0's sound "warm" or "cold"???? Either the cable 100% correctly passes the right digital sequence... or it does not. Period.
At which point, Group 1 usually replies that the optical plug is less reliable, they fall out, etc.
Then, the argument degenerates into bashing, and sometimes attacks even get personal.
Bottom line? If you believe you can hear a difference, then it matters to you. If you don't, go with what works out easiest. If you can use both, try both. See if you can hear a difference. If you believe you can, then buy what you believe.
Sorry to be vague, but it is a huge can of worms!