Ease of Drawing, Re-Holstering, and Attachment
When it comes to carrying, it is critical that you choose a holster that is easy to develop muscle memory around drawing and re-holstering.
In general, KYDEX and leather are much easier to draw from than nylon.
Leather, however, is much more difficult to re-holster than KYDEX. Attachment is also important. Many holsters require that your belt run through them, which is not convenient or comfortable for driving or sitting.
Many KYDEX holsters have a quick-release option that allows them to connect into a clip that sits on your belt. These can be handy if you are traveling or would want to carry once you get out of your car.