Digital Coax, optical, or RCA for use with my Bluesound Node player?

I have a Marantz 8805 and use the Bluesound Node 2i to enjoy my music on. 
I’ve listened to the Node with both optical and rca and actually prefer the node using the RCA connection. 
I’ve never tried a digital coax cable.

Which cable would you choose?
You'll do a lot better with a 75ohm digital coax vs. RCA interconnect. What is your budget?

I've auditioned quite a few. Acoustic Zen was very good.
Cerious Technologies makes a good S/PDIF cable with a return policy.
BTW, the recommended length for digital coax is 1.5 meters. 

I picked up a Audioquest Carbon digital coax
Analysis Plus "Digital Crystal" COAX 1.5M

Continuous Cast Copper (solo crystal copper) braids, hollow oval design. Demo’d and owned various AQ, AP, Cardas in 1m and 1.5m and preferred AP Digital Crystal. Pricey, but this to a good DAC and wallah!