the sound quality is the same.
the signal is just being sent through a different medium. one is through electricity, and the other is through light.
it basically boils down to what your equipment allows. alot of htib limits you to only a few of each...and you'll have to live with that. most videogame systems have optical so save the coax for your cable box.
for long runs...use coaxial because the cable is made for longer runs. for short runs, you can still use coax (to save some money) or optical (if it makes you feel all warm and fuzzy inside).
I was wondering which delivers better sound quality for a home theater system - digital optical cables or digital coaxial cables?