I personally have a preference of Kydex if I am using an IWB holster. The reason is the Kydex doesn't compress and make it hard to reholster your gun. For OWB I prefer leather. Leather just seems to work well and it looks nicer than Kydex for OWB.
I'm currently using a prototype handmade one I've made out several "soft" fabrics. (It is a crotch holster). neoprene with exterior liner of this stuff.
This waffle fabric has a great "non-slip" property that allows the gun/fabric/holster to stay put and it works the other way around also...it keeps the complex pants/underwear/holster dynamic from moving around.
This holster is only practical for deep conceal though. I can draw fairly quickly but you don't keep a round in the chamber and you will not win a quick draw at high noon in the middle of the street.
I really like leather holsters for comfort and because they are not hard on the gun finish. I also have been making my own out of leather and really have a lot of fun making holsters.
I like IWB holsters because they work best with my frame/build. I have a buddy that makes great thin kydex holsters that are extremely comfortable and secure. When I carry OWB, it's always leather though, mostly Galco Concealables.
My only other holster is a neoprene/fabric pocket holster for a PM9. Works great in dress pants.
I have just recently started buying better holsters for my carry guns. Up to now I've been using those nylon "tactical" holsters that can also carry an extra magazine. I'm sort of still going back and forth though. The inexpensive nylon holsters have been getting the job done for years, plus I can add another magazine.
But I have to admit that leather holsters, designed specifically for the model handgun, have been a tad more comfy and less bulky. I normally carry IWB, cross draw.
Plus, I like leather. I believe that a leather holster might limit wear and tear on a gun's finish (true/false?)
Depends on how much crap gets embedded in the leather making it abrasive. If you only wear it for dress (not training) it would probably stay clean and smooth longer.
Kydex stays smooth and is easier to just wipe down after you've muddied it up shooting in less than favorable conditions.