Technically Coax is supposed to be better over short runs and Toslink (optical) over longer runs due to the possibility of interference in longer runs of COAX cable. A digital signal traveling over fibre optic cable is (supposedly) less susceptible to interference.
Personally I won't have an optical cable in the house! I've always found no matter how good a cable you get (I all think they sound the same!) they have a harsh sound to them.
Coax is the best IMHO. Reason....See above.