Optical Vs. Coaxial Digital - Which Interconnect?

I have both connections to my preamp and have read different things about both types. I recently began improving my interconnects and speaker cables and there was some obvious improvement in the sound.

Anybody have any thoughts on coax vs. Optical digital connection to dac/preamp or any web links to articles?
you should look this up in the archives. You'll find many threads. All the high-end companies recommend coaxial connections, but there were a few people writing in that claim optical sounds better. Remember that the signal has to be converted to optical and back again on the other end. That has got to add noise and jitter. I prefer coaxial.