Well, for an ourdoorsy holster, I prefer Nylon or other synthetics. The primary reason is that Nylon is easy to clean, and won't crack or lose shape when it gets wet/dry/wet/dry, etc. Dirt or grit in your holster will cause finish wear on your gun as you move around, and may even scratch it rather severely during a draw. Nylon and the other synthetics can be cleaned often enough that it is less of a problem than with the (admittedly nicer looking) leather rigs.
Less money, too, if that's important to you.