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

@jumia   At one RCA connector shield and negative/return wire are both soldered at the base of the connector while signal/positive wire is soldered to center pin.  On the other side only two wires are soldered while shield is left unconnected/floating.

Since you are only concerned with single ended RCA interconnects with coaxial cables, I will share my experience with you.  

For many years I used a fine 75-ohm Belden #9259 oxygen free single center conductor coaxial cable with a bare copper braided shield over a polyethylene foam dielectric.  This was my principal preamplifier output to my mono block power amps input for many years.  I really had no complaints.  Due to a change in my room arrangement, I was forced to construct new & longer interconnects.  I was unable to acquire an adequate amount of the Belden #9259 cable without purchasing an entire roll.

I did however receive a timely tip from a respected analog guru.  He recommended Mogami W2549 coaxial cable which has 2 OF center conductors + bare copper braid.  You can experiment with it in 2 methods: 1) solder 1 center conductor to the RCA + cup, the other center conductor to ground & the bare copper braid as the shield or 2) solder both center conductors to the RCA + cup & the bare copper braid as ground.  Interestingly, the company that I purchased the cable from (Redco) actually terminates them per method 1 (above).  However, I chose the second method.

I made my main pre to power amp interconnects 25' long.  2 more pair 1 meter long and a 4th pair 2 meters.  After about 300-400 hours of "run-in" I was more than pleased.  Doing this project requires some good tools, materials and diligence or alternatively, pay someone or business to do it.  If you are a DIY person, you may wish to select an RCA connector with a crimp connector option for the braid so that you only have to solder the center conductor(s).  I found that soldering the braid to the ground of the RCA connector to be the most difficult part of the process, mostly because the RCA's that I chose didn't leave me much real estate to work in.

I was not able to compare these particular Belden vs Mogami coaxial cables in my system fairly, but I am very pleased and settled with this decision & execution. The Mogami cable is exceptional in every aspect with vivid detail and dynamics.  

I hope this has provided some limited comparative insight.

Best luck

I like Mogami too. I have their 3173 Cable as a interconnect between amplifier and preamp. This is a little thicker than the 2549 and also has a drain wire Plus 2 conductors. In this situation the drain wire is connected to both sides.

Still breaking in and thus far it’s a wonderful cable and very inexpensive.

I've heard inexpensive star quad from Straightwire that Excell.