For what it's worth, my experience with the questioned platings. Others may have a different experience with them.
<b>1 - Silver (plated and solid sterling)</b>
There is a lot of confusion about this one. The only Sterling available are those kits from Berea. They are solid silver alloy. The others are called Sterling, but they are really Silver Plate. Ask any woman familiar with flat dinnerware and she will tell you the difference.
All Silver tarnishes, and it has to be polished if you want a bright finish. Silver plate wears off, and the more it is used or polished the faster it wears. The secret to durability of a Silver plate is the thickness of the plating. At the prices for the kits, it can't be very thick. My experience is that it wears better than 24k Gold, but not as good as the Titanium/Gold.
<b>2 - Bright copper </b>
The answer to this one is easy. Copper is Copper. It is soft and it tarnishes. It can turn my fingers green. The Copper can turn green. I know that it has other alloys, but my experience is that if there is enough Copper that it has the color of Copper, it will act like Copper. My experience with a couple Copper pens was no different.
Some of the kits have a lacquer coating on them, but that wears off rather quickly. Some folks have reported good results with a clear powder coating.
<b>3 - Satin copper</b>
No different from the bright Copper. The only difference is that it has a brushed satin finish.
<b>4 - Gun metal</b>
This depends on what it is. I had a pen kit several years ago that was an honest-to-Gawd oxide finish on steel, and it wore about like I would expect from a blued rifle barrel. I have no idea where it came from. The most recent pen kits have had a painted-on coating that very thin, scratched easily, and wore off faster than a 24k Gold.
<b>5 - Black chrome</b>
It doesn't matter whether it is bright or black, Chrome is the hardest and most durable plating that is put on a pen.
You didn't mention Titanium/Gold or the Titanium or Rhodium platings. Both are more durable than any of those you asked about, other than Chrome. I think that their quality is reflected in their higher price.