Digital Output, Optical or Conventional Coaxial?

Just curious about this, which digital output, optical or conventional coaxial, do you prefer to use from your CD, DVD or Blu-ray/HD player do you prefer to use when connecting to a processor? Why do you prefer one connection over another?

Personally I use the optical digital output from my Pioneer Elite BDP-94HD player to connect to a Krell 7.1 HT processor. Sonically, there is no obvious difference between this and the conventional coaxial link. However, there is absolutely no hum on the optical cable link.
optical from hdtv tivo, coax from cd, component digital from dvd---why? cause senior engineer at mcintosh told me to do it that way.....some people i listen to....
Duh. What is component digital? Is there a principle hidden in these recommendations? In other words, why?

Sound wise I have found them to be all the same. Choice dependant on the gear outputs and available inputs on other gear in use. I have some components going into two others. Such as tv and preamp etc.
Digital rca cable will always beat out optical soundwise but optical precludes any ground loop issues common from cable boxes and such.

When you connect your CD player via digital out you essentially by-pass its DACs and use the DAC in your pre/pro. If you use the analog rca, you will be using the DACs in your CD player. So it becomes a matter of which componet has the better DAC and which sound you prefer.

On Blu-Ray DVD, you must use the HDMI to get the new HD audio codecs inhernent in these recordings. If regular DVD, use can use the digital audio out to your processor. I run the component straight to the TV as I don't have HD/Bluray DVD and the digitial audio out to the processor. Same with the TV, I run an digital from the cable box audio out into the digital audio in on the processor and high end component cables from the cable box to the TV.

Most all newer LCD/Plasma have an digital out but it is optical and the HDMI output for the Bluray audio codecs.
I was using Optical on my DAC, because it did sound better than the coax in on the DAC. This should not be the case - in fact it should be the other way round.

I then picked up a pulse transformer made for digital lines and put it on the RCA input on the DAC. This made a significant difference, so much so that the optical connection now sounds like crap in comparison.

Sometimes it's the little things that are left out of components for budgetary reasons that make the most difference.