What's better, one conductor or two conductors for an RCA interconnect?

https://www.conch-house.com/best-rca-cables-audiophile/

these are assorted RCA cables. All have a positive and a negative. I’m not sure I’ve ever seen a a RCA cable that doesn’t use both.

All the best.

optimize and oldrooney I learned a bit from both of your responses. I have a purely digital system (can't afford analog). My integrated amp has three connection options (no XLR go figure) so for the fun of it, I have my CD player connected via line stage, coaxial, and optical. Switching between the three my 75 year old ears cannot distinguish the difference between optical and coaxial through my system, the analog line stage as you would expect is inferior to both. 

I was under the impression XLR was the best followed by coaxial, optical, and then line.  

@tcotruvo, coaxial cable is also the cable of choice in almost any scientific application. My understanding is it is better for electrostatic noise rejection but there may be circumstances where shielded twisted pair is better for magnetic. I am going off memory here. It depends on the shape of the noise field. Primary reason for not using co-axial is it is difficult to work with and maintain its properties.

I would expect you would have to have pretty long runs before cable capacitance became important. I am sure there are some bad tube products that could have issues.

A French audio journalist named Jean Hiraga wrote the paper that proposed using 2 identical twisted wires with a shield that was only connected at one end as a way to assure the waveform being conducted was treated with the same impedance for both positive and negative polarities. This idea was picked up by Noel Lee and his team at Monster Cable and marketed as “Balanced Bandwidth”. They added the prescription that the cables were directional based on which end the shield was attached, and put arrows on the cable. This approach has become entrenched and is accepted as received wisdom by many cable manufacturers today…but not all. Prior to this, virtually all RCA interconnects were coaxial…meaning a center conductor was wrapped with a shield of braided copper separated by a foam dielectric. 
I’m not claiming to pontificate on the validity of this article of faith!

Interesting @crustycoot .  That journalist no doubt discovered what was already being used industrially and in the scientific community no doubt for decades prior.