I too make holsters,,,
My experience has been that the worst wear comes from Nylon holsters,,,
I don't know if it's naturally abrasive or just holds grit and becomes like sandpaper,,,
But almost all of the LEO's I have worked with over the years have experienced faster wear after switching to nylon duty rigs.
I (being a leather guy) despise Kydex,,,
It's just a personal prejudice of aesthetics I have,,,
I have noticed at my range that every pistol carried in a Kydex holster,,,
Has very specific points of wear on the flat and sharp points of holster contact.
Unlined leather molds to the pistol very nicely so point of contact wear is minimal,,,
They have the same problem as nylon holsters though,,,
They need to be cleaned regularly,,,
or they will collect grit.
Holsters lined with top grain leather are the easiest on your gun for holster wear,,,
Simply because they do not hold grit and are easy to clean out,,,
Just a wipe with a damp (slightly damp) rag or sponge,,,
And a small amount of saddle soap.
The ones you want to avoid at all costs are suede lined holsters,,,
They hold grit for one thing, but the main danger is that suede leather,,,
And most garment/upholstery leathers, are often tanned using chromium salts.
If your holster collects even a little bit of moisture,,,
It will not be long before the residual chromium salts start a chemical reaction with the blued steel,,,
This should be a no-brainer in that you should never store a gun in the holster for long periods of time anyways,,,
And certainly not in a holster that is even slightly damp.
I have seen that bad reaction start in as little as 1 day in suede lined holsters,,,
I've even seen it damage stainless steel guns.
Hope this helps,,,
Aarond