which are the best headshell wires ??

The wires you like the best.
I would seriously only consider headshell lesds which have really good clips such as, silver over copper for instance, as for the wires themselves. I would think a very pure silver would be best followed by copper. The only name brand that occur to me at the moment is Cardas.

Are we speaking about Rega arm mods by any chance?

Oyaide makes some high quality leads...you can get them from the cable co dot com