As a firearms instructor, gun store manager, private investigator, competitive shooter, and all-around gun nut, I have had occasion to use many types of holsters for multiple purposes over the last few decades. Many of these holsters are quite specialized and therefore currently reside barely used in boxes and drawers in my cluttered gun room. A very few favorites are nearly as well-worn as my years-old leather wallet, and with them I feel the same intimate familiarity. Broken-in and supple, I hardly have to think to put them on or draw or reholster.
If you live in a CCW (concealed weapons) state and carry a gun daily and are lucky enough to grow old with such a holster, you win. Like a cowboy hat or a good pair of boots, it takes a lot of everyday use to get them the way you like them, and they become very personal.
But holsters are used for many different purposes. For years I competed in IPSC (International Practical Shooting Confederation) shooting a stock Glock with nothing more than a sturdy wide belt, an inexpensive Uncle Mike's #15 holster and a double mag pouch with all straps removed. I sometimes still use these today, and I can't give a higher gear recommendation for cost versus quality for this purpose.
Another slick and inexpensive option for competition is anything made from Kydex or plastic or whatever the manufacturer wants to call it. They are fast, often adjustable for cant (the angle of the gun in relation to your body), and nearly indestructible. My Fobus paddle holster has had thousands of draws from it and is nearly as good as the day it was born.
Leather has been the most common holster material since forever, and there are many quality levels. South of our border you might find urine or brain-tanned leather with great prices but with questionable stitching that might last a few draws, or with dye that will bleed all over your body, clothes, and gun the first time you perspire. Or you can pay a heftier sum and get a quality horse-leather product made by artisans at places like Galco that will last you lifetimes. The most beautiful holster and belt combination I have ever seen was a Western rig made by Galco for President Reagan.
Modern molded holsters made of plastic, Kydex, carbon-fiber, or other synthetic materials are weatherproof, light, relatively inexpensive, and wear-resistant. These are great holster materials for the non-traditionalist, and are fast catching on with most manufacturers. Beware, some molded holsters will wear the beautiful blue off your fancy new pistol slide in short order.
I carried a handgun in the thorny bush of Africa in a plastic holster without fear of moisture retention or the gun falling out even through some harried climbs and inadvertent cliff-diving. Indeed, the human body is much more susceptible to breaks, bruises, and scratches than a sturdy molded holster. Not much to look at, but extremely practical and functional.