The custom kydex when properly fitted to the firearm is quite and that is one of the reasions that I am up grading from a retention style kydex like the Serpa.
Didn't you know those things are dangerous JMac? Tex shot his self because of that stupid trigger lock.
So Kydex vs. Leather. This is going to be hard, I really like leather.
Kydex doesn't get wet, the holster stays open, can provide retention via fit and friction instead of snaps and straps, you ever fall onto a holstered pistol?
I know there are more reasons, I'm not very creative this morning.