What's the best plating material for interconnects plugs ?

Does anyone has opinion on whats the best plating material for connector plugs, is it silver, gold or rhodium ?

Clamped OCC copper!
From your list, probably silver. I believe oxidized silver is as good a conductor. I’ve seen copper connectors. Not sure how they hold up with all the air. Gold is probably okay for longevity but it’s not a great conductor. Sounds warm. Rhodium is great for detail but can sound a little hard and chrome-like.
I'm on rhodium clamped and monster cables, I have a lot of details but my new preamp is totally balanced now so I was wondering if I could improve sound by changing wires 
Definitely not Rhodium as it’s a far inferior conductor to the others. Silver is best since oxidation doesn’t inhibit its conductivity for all practical purposes.
Rhodium is a poor conductor and very hard. These are not qualities you want in a connector interface material unless you can be assured the mating surface is soft. Two rhodium surfaces would be the worst of all worlds.
OP the question is WHY do they plate the terminal end to begin with?

After you find out it’s always for protection and or issues with growing barnacles, make a choice.

Above copper are super conductors. Silver is the only one I know of.
Copper at 100% Silver 105%.

Nickel/silver or just nickel use to be and still is popular.. Silver, Copper Gold, for me

Tin over copper if I’m gonna bury the sucker..

Everything below that is for corrosion or just being pretty. Gold is warmer than Rhodium, it’s just a better conductor and not so hard. Rhodium is actually to strengthen and add "Spring" to materials that don’t recover well from being mechanically coupled. Say a male bullet into a female bullet connection, Rhodium acts as torque retainer for contact pressure.

This is where contact enhancers come into play. Without getting all techy there are fields being formed through materials and because of materials. By reducing the resistance between contact surfaces, we net the TRUE sound of the cabling and terminal ends, NOT encumbering the sound with a LACK of good contact..

There IS a reason terminal ends and cabling "SOUND" different.

Materials can act as minor tone controls, get to know the materials your using.

Copper is always good, you have to work at it to make copper sound BAD.. Really you do.. NOT BAD but it can be GREAT... there is a difference..

What the wire is covered with.. Holy cow...  I like teflon.. just good all around performance, last forever and not easy to harm...

Just to clarify where several posters have stated that silver oxide is a good conductor, That is simply not true. Silver oxide (Ag2O) is not a conductor but a p-type semiconductor with a band gap of about 1.2 eV, so conductivity is about 1/1000 that of pure silver.

However silver oxide does not readily form on the surface of silver. The typical tarnish on silver is silver sulfide (Ag2S) which is also a semiconductor with a band gap of about 0.9 to 1.1 eV. So for both the oxide and the sulfide, the conductivity is poor compared to pure silver.
choice is clear, silver it is ! thank you all for fantastic write ups and all of you help !
Most small RF connectors are beryllium copper, tellurium copper, or brass with a gold plating for corrosion resistance. Same for audio connectors. While gold is not the ideal conductor, it's better in the long run than other materials that decay and corrode. 
Just to clarify where several posters have stated that silver oxide is a good conductor
@ljgerens Thank you for the correction. Ironically, I read that misinformation on Audiogon.
In my experience it's down to how good the contact is and whether it gets disturbed. If it's clamped tightly and rarely moved then copper or sliver are fine, if it's a press fit (like RCA, XLR or banana) then gold on gold eliminates worries about corrosion and the softness of the material ensures a good contact surface area. There is no benefit from using rhodium outside of a caustic environment. 
@ssg308 -  one approach to connector selection is to consider the conductivity of the metals being used

Please see this link that shows the IACS conductivity rating of various metals
IACS of Metals, Alloys and Solder (avoutlet.com)
  1. Silver 106%
  2. Copper 100%
  3. Gold 76%
  4. Rhodium 39%
  5. Nickel 24  %
However - when plating - for the plating material to "Stick" to the actual metal of the pins of a connector, many times requires a substrate plating that has an even lower IACS rating

This generally means the connector will not provide the best possible performance

However - Silver Plating onto Pure Copper requires no substrate and therefore provides the best combination from a conductivity perspective

But beware - some "silver plated copper" connectors are actually made from some type of copper alloy, like Beryllium copper, which is not as conductive as pure copper, but it is more robust

What about the black tarnish? - Some people regard the black tarnish that often develops on silver (plated) connectors to be a problem. But in reality, the tarnish is only microns in thickness and can be removed simply by reseating the connector. The tarnish is regarded as a "semi conductor", so it will conduct electricity, but not quite as well as silver.

Unfortunately it is also not as simple as selecting the best IACS ratings for the various materials

My current RCA plugs are silver plated copper and they outperform many solid silver connectors. So metals are not the whole story either.

I have found the best connector uses pure copper as the base material and silver for the plating and all my connectors on all my cables are created in this manner

Gold and Rhodium has a certain "image", but they both pale in comparison to a good silver plated copper connector when it comes to sound quality.

Just another opinion - Steve :-)

If the base metal is garbage, it doesn't matter what exotic metal is plated on it. Throw in plastic for the insulating/molding parts and the problem is compounded even worse. One gets what one buys...
@williewonka +1
Great advice given.

My only add would be to mention a couple of brand names such as Vampire Wire that used direct gold plating over copper and their upper Xhadow line that used direct silver plating over copper.  Unfortunately, Sound Connections (the parent company of Vampire) recently closed their doors and Partxconnexion purchased the remaining stock and the rights.  
ETI Research also has some nice designs.
I was under the impression that silver plating directly on copper is not a good idea. Copper readily diffuses into silver and forms a copper/silver eutectic layer which negatively affects adhesion and electrical conductivity. Typically a copper surface is pretreated or a barrier/adhesion layer is deposited before the plating of silver.

Any amount of visible tarnish will reduce the surface conductivity of silver. A micron is a lot of tarnish. A micron of tarnish can reduce the surface conductivity of silver by as much as a factor of 1000.
@ljgerens - I do not know the science that goes into plating, but these guys seem to now about the Silver plating onto copper in the field of electronics
Silver Plating of Copper or Copper Alloys - Advanced Plating Technologies

They appear to confirm what you have said - almost to the letter

But they also state that for "pure copper"
The copper can then receive a nickel underplate (if specified) followed by a silver strike and finally the silver plating. The silver strike layer is very important to achieve an adherent silver layer and avoid silver immersion that would result if the copper was immediately silver plated without a strike.
So the nickel underplate seems to be optional and the Silver strike takes care of adherence

But on the more practical side of things - I trust my ears and after many years of listening to different materials on a variety of connectors I find the following to provide exceptional performance
  1. KLE Innovations Absolute Harmony Silver plated RCA plugs
  2. KLE Innovations Harmony Silver plated Banana
  3. Sonar Quest Silver plated Copper Mains and IEC connectors
Keith Louie Eichman has spent a lifetime (close to 40 years) making connectors and cables and it seems he has an affinity for silver plated copper and based on the excellent performance of his products - he must be doing something right.

And I am yet to find any connector that will compete with the dynamic performance of these connectors at a similar price point

With respect to tarnish - none of my connectors are exhibiting any signs of tarnish on the "contact areas" of the plugs and that is after approximately 6 years of continuous use.

Tarnish will only occur where an area is open to atmospheric Sulphur and due to the lack coal fired electricity up here in Canada the amount of Sulphur appears to be minimal
  • e.g. The areas of the Banana plugs I currently use that is exposed to the "air" is only recently started to colour a very faint brownish tinge
  • But the area inside the binding post is still very white.

For folk out there that dislikes the thought of any tarnish buildup I would suggest you use Gold.

Personally - I would ONLY choose Rhodium if there is no other option.

But that’s just "my personal preference"

Regards - Steve

A silver strike is one of the pretreatments that I was referring to for the proper adhesion of plated silver on copper. A silver strike is typically a very thin deposition of silver (fraction of a micron) from an electrolyte containing a low concentration of silver ions and high concentration of free cyanide as a complexing agent. From my experience these coatings do not produce a pure silver layer.

By the way, burning fossil fuels is not the only source of sulfur in the atmosphere. Sulfur is also released from the decomposition of sulfur containing organics and from volcanic activity and geothermal vents. So there is plenty of sulfur in the atmosphere, even in Canada.

@ljgerens - good to know, but it will not change my mind about Silver plated connectors. They are simply my preference

But others are free to choose otherwise on reading your posts above

After all - We are each entitled to an opinion.

I was not trying to change your mind.

I was only trying to point out the inaccuracies in some posts regarding the surface and interracial chemistry and electronic properties of silver and its corrosion products.