The type of holster about which I am speaking is a strong side hip holster with at least one retention device. Inside or outside the belt does not matter, that is so long as you can easily draw the weapon with one hand (either one regardless of on which side you keep the holster) for firing, and you can easily re-holster the sidearm with one hand (either one regardless of on which side you keep the holster), and then engage the retention device (if not automatic) with that same hand. So what does that mean in holster selection. Well first of all it means quality. Don't by a cheap nylon or leather holster and expect it to remain good as new after using it for awhile. Do buy a quality leather, nylon, or plastic holster made by a reliable manufacturer. The specific traits you want to look for in a holster are as follow:
1) Quality - stick with a good name brand of holster, one that is fair to higher priced. Don't go bargain basement shopping when your life may depend upon the quality of your holster.
2) Material - leather, or ballistic nylon, or plastic (possibly polymer). I prefer a leather holster. From what I have seen in based on holster I and others have used, a quality leather holster is king. Nylon is okay, but ones I have had always wear out before a good leather holster. Plastic holsters are the latest thing I guess, but I do not like em at all. They are noisy and can click on things when you are trying to move with stealth. They are also noisy on the draw, and you may just want to be quiet sometimes when you draw a gun. Some of them, even ones believed to be of the highest quality, have been shown to be easily torn from a belt. A leather holster, with proper construction, is something that will last many years. With proper belt loops it is almost impossible to take a gun away from a shooter by ripping off the holster. It needs some care as in cleaning, and conditioning over the years, but leather is well worth the small task of doing such. They are also repairable.
3) Design -
a) As I said, I prefer a strong side (right side if right handed, left side if left handed) hip holster. When you draw from a strong sided holster, with your regular shooting, or strong side hand, you do not cross your body in any manner, you do not cross a field of fire that need not be crossed with the muzzle of the gun; you pull it out, and if facing your adversary, you have it on target almost as soon as it clears the holster.
b) I also prefer it to have at least one retention device. The retention device that I prefer is a thumb break/snap (not Velcro), although I will readily admit there are other holsters that have more secure retention devices. My reasoning is this: I want the gun to remain in the holster is I run, jump, climb, fall, grapple and so on. I want something to prevent immediate removal by a bad guy who tries to take my gun from my holster, something that gives me enough time to make a defensive retention move, but not something that slows down my draw. This is a thumb break holster.
c) I want a holster that remains in an open position after I have drawn the firearm from it. In other words, I do not want a worn out old holster in which the slides sort of close, or collapse inward, once the gun is out of the holster; nor do I want a new holster that does the same thing. Cheap nylon holsters are notorious for this. My reasoning here is that I want to be able to re-holster my sidearm with one hand, and then secure it with the same hand. Why - well because it keeps the other hand free for close in defensive moves if needed; and another thing is that is one hand is disabled, you can still secure your weapon with the other hand. Now mind you, I do not want a loose fitting holster, I want one with a snug fit, that is form fitted to the model of gun I am carrying, but it must be one in which it is easy to re-holster one handed.
d) Angle of the holster - I want a holster that rides high on my hip/belt, and wherein the firearm sits in an almost perpendicular position to the ground when I am standing up erect on level ground. I do not want a holster that tilts to the front, or to the back. Such holsters are not as defensible during gun retention moves. I can also draw from just about any position in which I find myself with such a holster. This includes prone on my belly or back, lying on either side, standing, sitting (even while seat belted into a car), or standing on my head if need be.
e) Belt Loops - these should be large enough to accommodate the type of belt you will be wearing. In addition they must be strong enough to withstand the gun take away efforts of a really big guy who grabs the whole holster, with pistol in it, and then tries to tear it off of you. Don't think it can happen, well then think again. I have witnessed this more than once. While on this subject, think too of the belt on which you secure your holster. Use a good quality belt, nothing fancy, but one that is made well and strong, with a secure buckle.
f) Lined or Unlined - this is a question that arises only in regard to leather holsters as far as I am aware. I prefer lined holsters as they are easier on the finish of the gun, and they are a bit thicker than unlined holsters that would otherwise be the same. This extra thickness seemingly adds to the durability of the holster over the years, and helps keep the holster open when the gun is removed.
g) Trigger covering - any holster should cover the trigger and trigger guard when the gun in in the holster.
h) Open or Closed Bottom - I prefer an open bottom holster. This is mainly because I do not want foreign material building up inside a closed bottom holster which could eventually plug the muzzle. Things like dust and lint (lint is a bad little booger in winter months when you wear sweaters). I am the forgetful type at times, and while I usualy check my equipment, one thing I would likely be to forget is to see if a closed bottom holster had debris init each time I put it on. With my open bottom holtser, I see if it is clear each time I pick it up because light comes right on through. Just simpler, closer to foolproof.
Holsters such as shoulder rigs, ankle holsters, thigh holsters, all may have one or two advantages over a strong side hip holster. For example an ankle holster may be more easily concealed. A shoulder holster rig also may be more easily concealed, and a thigh holster may give you a speedier draw. The thing is, that each of them falls short in more than one way or another. Ankle holsters are very difficult from which to draw while running or even walking fast towards something like cover, they are also the lest defensible when it comes to weapons retention. How do you hold onto a gun in an ankle holster if someone grabs your leg and tries to take it away. Sure you may do it, but you are much less likely to retain it than would you be had the firearm been in a strong side hip holster. A shoulder holster rig can be a blessing, especially if traveling in a plane in those tight seats for an LEO. The thing is though, when you draw from a should holster, you telegraph that you are reaching for a weapon. You also are performing a cross draw, drawing from weak side, and bringing the gun across to the strong side. It is a slower draw than from strong side, and such a draw causes the muzzle to cover things it quite possibly should not be covering. As for a thigh holster, you know the ones I mean, the ones SWAT guys wear. They are just about useless from what I can tell except they add speed to the draw in most cases. The thing is though, they are not as defensible as is a strong side hip holster, and they apparently often cause guns to go flying. I have seen guns routinely come out of these (several brands) while LEOs were training in tactical shooting that required running. If you feel it start to go, and this often happens, chances are you likely will not reach it in time to retain it on your thigh. if you feel a hip holster open, the body often keeps the gun retained, and just putting your arm against your body can do the rest.
The following paragraph was added on October 9, 2007: I did not mention carry in a pocket holster, but I will say here I do not like the form of carry because of how long it takes to draw, and how inaccesible is the firearm if you are in certain positions such as seated. Pocket carry without a holster is even less preferable than with one because of the potential for forgotten foreign objects in the pocket to interfere, jam or plug up the firearm, or to possibly even cause it to fire.
***************************************************************************There may be more that I will add later on, but for now that it is. Whether you carry openly or concealed, this is the type of holster I recommend. About the only consideration that I would go beyond on suggestion I made above is if you might want a holster with additional retention devices, or with a different retention method. Of course, whatever you get is up to you, take my opinion or leave it, it does not matter to me. Just do yourself a favor, carry safely and practically.
All the best,