what is better digital optical converter or hdmi converter

If you're near the end of your signal chain and you're wondering at what point you should finally go out to analogue - that will depend on the quality of your DACs and your cabling*. (I'm assuming here that the digital connection is working within its design tolerances and is transferring the digital values 100% accurately, which should be the case most of the time - though it is possible to have issues with deficient cables, incompatible clocking, etc.) There's generally nothing to be gained from converting to analogue and back to digital again most likely, you'll only lose quality that way. If your receiving device is going to convert the sound to digital again internally, then you should connect TO it digitally if you have the option.

Is there a clear and general 'best' option for connecting the devices, is it basically the same either way, or does the answer depend entirely upon the specific devices being used?

The source device has RCA and optical outputs, and the receiving device has RCA and optical inputs.

Both devices are of reasonable and approximately comparable quality.

The distance between devices is < 50 feet.

The source audio is stored digitally (as MP3, FLAC, etc.).

If there are caveats that require assumptions to be made, then please assume something along the lines of:

The question is more about which, if any, preserves a more accurate signal (as measured by the difference between the played/recorded sound on device 2 and the original source waveform generated/sent from device 1) between two devices. I've seen similar questions raised elsewhere, but they usually just end up with someone stating that a digital connection will get you more channels/speakers and is therefore 'better' however that's not really the question. All other things being equal, if there's an option for connecting two components using RCA cabling or connecting the same two components using an optical cable, is there any reason to prefer one method over the other from a pure sound quality/fidelity perspective?

What is better digital optical converter or hdmi converter