Without knowing a budget, the best of the best in terms of UPOCC copper would be the Effect Audio Ares S 8W. In addition to the quality of the copper, the multi-strand structure of different diameters helps with separation and clarity without losing note weight. Personally, I don't have it, but I have code 23, which would be a further evolution, but not very ergonomic.
EA has also had a very interesting option as a special Christmas edition, in which they mixed the Ares S and the Cadmus (Silver Plated Copper). It seems that the limited edition has already been sold, but you can still order the cable, with the usual elements of the Signature series.