Fiber Optic vs Digital Coax 2pt. question

This is a two part question. First Ive alway's assumed that if you have your choice of a F/O cable and Digital Coax that you should use the Coax. Is that a true opinion? My second question is that I've alway's felt that it is more important when you upgrade your cables that your RCA's improve your sound more than replacing a Digital cable, like replacing your digital from your cd to your dac makes less of a improvement than upgrading from your dac to your pre amp, then your pre amp to your amp. I'm not sure but is that on the right track>
As far as my listening experience is concerned- and that goes back far beyond the beginning of digital - you are perfectly right on both accounts. I threw the F/O cables away in the eighties of last century and any experiment with that breed undertaken later ended in sonic desaster. I also agree fullheartedly with your second assumption. As far as my ears are concerned you are certainly on the right track!
I tend to disagree with part 2 of your question. I have found a larger variation in the sound of the digital interconnect and find this to be a very important interface. Just my 2 cents.