Leather...and plastic...are moldable and usually hug the body closer than a nylon holster. Nylon holsters are usually universal to a degree, bulky and fit a number of guns while a molded leather holster is built for a specific gun and usually only slightly larger than the gun itself. A nice leather holster also looks better.
Kydex...It's a fancy word for plastic. They work and they are not expensive. That's what I'm using now, but I'll probably buy something nicer when I run across it. Stores don't stock much for a G30 and I've tried enough holsters to know that if I order one without trying it, I probably won't like it.
Safariland has a nice thing called STX Tactical, which is probably the same plastic but looks like better quality. I have one of their 6367 level 3 holsters, but it's not for concealment.
Leather and guns have gone hand-in-hand for ages. I carry a leather holster, and there's no squeaking. I prefer leather over anything else when it comes to guns.
In order to rally people, governments need enemies. They want us to be afraid, to hate, so we will rally behind them. And if they don't have a real enemy, they'll invent one in order to mobilize us.
I use leather and kydex holsters, nylon is just too cheap feeling to me. The kydex is faster on the draw, but the leather just feels better to me although it is more expensive.
My pref's... Wheel guns: Leather
Auto's: Mil-spec ballistic nylon and kydex/plastic w/ steel belt keepers.
I open carry 90%... 'hot here... cowboy country. Not an urban/suburban environment. 'Stuff takes a beating. I use what works. Bianchi, Triple K, or military.