In theory, the XLR balanced configuration is superior. Line noise is rejected just like when using a balanced interconnect. TOSLINK optical is a complete waste of time because the SP/DIF signal is truncated for "consumer" grade TOSLINK. ST Glass optical is great because it carries the full SP/DIF signal *AND* electrically isolates the DAC and Transport. However, in my experience, the balanced digital links have sounded better. However, neither cable will stand up to the new I2S links. (I2S is a 15 pin link which carries audio and clock signals - the best implementation possible is the slaving of the transport to the DAC) Keep a look out for I2S and naturally don't buy balanced, optical or I2S before you listen to them all.
