Optical carries a digital signal (zeros and ones). Coax can carry digital or analog signals. Cat5 can also carry both and some people use it for more than computer networks (digital). It has been used as speaker cable connections (analog) as well.
Digital signals will carry the most true set of information as it is hard to degrade except over long distances. Analog signals are necessary for many applications (e.g. speakers) and will be perfectly fine as long as there are no significant sources of outside influence (e.g. do not place strong magnets or power boxes near analog wires in use).
