Think about it.
No matter what you choose, since there will be large gaps between the spacers, the vast majority of space between the cable and the floor will be air. Even if getting the cable off the floor does make a difference, what you use to do it can't be significant. Pick something that is pleasing to the eye since the ear won't be able to tell the difference.
I challenge you to try it with different materials and report back what you find.
No matter what you choose, since there will be large gaps between the spacers, the vast majority of space between the cable and the floor will be air. Even if getting the cable off the floor does make a difference, what you use to do it can't be significant. Pick something that is pleasing to the eye since the ear won't be able to tell the difference.
I challenge you to try it with different materials and report back what you find.