I need advice for power cords

In my experience the cable design will predict where placement is best.  Some is the source, others are the amp.  One improvement for me was Torus Power isolation transformer.  Modern power have a high degree of pollution from electronics even when you run dedicated lines.  This was my personal issue.  

Buying cable used is a great value.  I like Allnic ZL, Audience, Zen Wave.

I prefer Copper over Silver.  But this is entirely subjective.

In my experience after ripping out drywall for ceilings and walls running 4 dedicated lines  to a sub breaker box, my issues actually worsened.  

The AC power was that dirty in my house - in part from my own computers and electronics and in part from the regional grid - neighbors switch power supplies, etc.

This noise does travel retrograde.

Solution:  TORUS Power isolation transformer - I placed a 75A wall mount unit.   For those considering one and use tube amplifiers purchase a unit rated for 4x the measured power draw of your amplifiers.  If you system draws 10A, then a 40A unit would be appropriate.  

The other consideration is RF/EF radiation from LED lights and dimmer switches.  The dimmer switches (which function by rapid cycling current) create horrible AC noise that I measured polluting my dedicated lines.