Which is better Coax or Optical cables

Both can be good option and as advised by ahendler if you are choosing optical buy glass and not fiber,If you are buying
Coax buy a professional cable and not the cheap stock ones.

I am open for other options but I previously had a Exogal DAC between the Oppo 105D and the integrated and it was outstanding.  Had to sell it to raise some money but I am planning to do something in the next few months.  Just raising money and researching....

When you had the Exogal did you use coax or optical. Did you keep the cable when you got rid of the dac. Then use that cable firstt if you get a new dac
Alan

If OP intends to add a DAC with 105D, he should use USB not coax or optical because 105D can handle native DSD only via the digital USB input on the rear of the unit(not the USB input on the front!). When I did so, I found an improvement also adding Schiit Wyrd, or iFi USB filter unit.
If you don't care about DSD, then ignore my suggestion. Cheers,
Spencer

My vote would also be coax. So many brands available, but I would add Black Cat Cables to your list. These are designed by the same guy that designed the Illuminati digital cable.