I have a number of handguns. More importantly I live in Washington State and don't carry concealed. I do carry my firearms when I go out in the woods, hiking, hunting, fishing, etc.
Over here it rains a lot. For the first revolver I purchased (a nice Taurus 357 Mag) I have a custom made full flap leather holster that protects it completly from rain, dirt, branches, etc. I treated the leather with lots and lots of oil and some wax I use to use to seal ski-boots (decades ago, when they were made out of leather).
For my Ruger Blackhawks, I have some Hunter oiled leather holsters and some nylon holsters. I also have a surplus military "shiny something" coated leather holster and nylon holster for a couple of Norinco Tokarev 9mm's.
While I like the aethetics of leather, after a full day in the Washington rain and woods, the nylon is sure a lot nicer to clean up. After enough water, the leather just gets soaked and needs to be dried out carefully so it won't mildew and re-oiled. As a result, most of my recent holster purchases have been nylon.
The only thing bad, I can say about the nylon holsters is that none I have seen have full flaps that provide extra protection (but then not all of my leather holsters do either).
Therefore, I suppose the leather versus nylon decision may be a function of what the weather is like when you use your holster and what you do when you wear a holster. Good luck
