Copper, silver, or gold MC cartridge coils?

One is preferable over the other two, IMO, as chosen by the designer and user.

Not all cartridge brands give you a choice.

I was thinking of ZYX brand.

Has anyone tried all three types in one brand. And which did you prefer and what were the perceived sonic differences?

Just looking for opinions. Everything in art and audio is subjective.

To Add to the list of Coil Wires being used.
Aucurum Wire,
( Gold Plated Six 9's Copper) known to be used by 
Ortofon for approx' 20 Years in some of their designs.

Koetsu Urushi,
( have a model that has a Silver Clad ' not plated'  Six 9's Copper )

I have been impressed with Ortofon Cartridges that have coils wound  Aucurum , as a result I now own a Cadenza Black, that I intend on having rebuilt to a change of Specification.

There are also Cartridge Tag Wire Pins used of different Metals, 
I am sure the combination of Coil Metals and Pin Metal will also have an
Sonic Signature.   
   

Since you asked for ZYX:

 I can say that tried both Silver Coil (Airy 3) and copper (Premium 4D) I think the last one (copper) is better, you can’t go wrong with copper coil from ZYX. 

Silver is definitely not warmer. 

For ZYX  i would prefer copper coils though silver could match rock pop material a bit better.
Never heard any of their gold model so i cannot comment.
@chakster 4D is somehow different to Airy so coil material there would not be easy to compare.
I agree though that you cannot go wrong with copper.

G