Holsters and Retention Levels.
First off, retention levels explained.
Level 1: Friction only. Example - Raven Concealment Phantom and Crossbreed IWB holsters.
Level 2: Friction + Button/Release/Snap. Example - Safariland ALS only, SLS only or the Blackhawk SERPA button only.
Level 3 and 3+: These holsters are Friction and at least two forms of button/release/snap/etc. I.e. Friction, SLS and ALS retention. Some holsters have the three retention forms plus an additional “feature” where you have to pull the gun out a certain way to remove the gun from the holster. Stay away from Level 3 and Level 3+ holsters.
Now for an explanation of holster features + needs.
*Never use a “universal fit” holster for a gun that may save your life or the life of another. Not only will the holster not hold onto the gun in the holster well, but it will not allow secure single-handed reholstering.*
Level 1 only. It’s concealed, so your cover garment is the additional level of retention.
For OWB concealment I prefer the Raven Concealment Phantom LC models.
For range work, holsters like the CompTac Belt Holster or Bladetech Sting Ray Belt Holster will work, but will be bulky for concealment.
For IWB concealment I have used the Raven Phantom and the Raven Vanguard 2 (VG2) as well as the Crossbreed Supertuck.
I am a fan of Appendix carry, especially for any time spent in a car. The gun will be much easier to retrieve whether you keep it concealed or not. The VG2 is the best minimal holster for this use around.
For traditional 3 or 9 O’Clock carry, the Crossbreed SuperTuck is very comfortable, but does have the following issues in my experience. First, the comfort of the holster slows down your ability to obtain a fighting grip. Yes, its minimal slowing, but that could be the difference between life and death. Second, the factory belt clips. For IWB, a clip attachment is easy, but not ideal. You should have a loop of some sort to lock the holster to the belt.
I've also used the Peters Custom Holsters "Hold Fast" and am impressed by it. Only thing I noticed as a negative was the lag time in holster ordering and a lack of a firm shipping date. Other than that, nothing to complain about the design.
Open Carry/Duty/War Belt/SHTF use:
I will only run the Safariland ALS system for this. It’s secure and doesn't have your trigger finger do anything other than pressing the trigger when needed. The ALS retention is deactivated during the acquisition of your grip, minimizing grip and presentation issues for shifting from a CCW/Off Duty carry holster to a duty holster.
For Duty Belt/War Belt carry:
Safariland ALS 6390 series of holsters. Available for all common duty guns (i.e. Glock 19/17, M&P 9/40 or 1911’s) with common lights – X300 or TLR-1’s. The 6377 and 6378 series are the direct to belt via belt loops or paddle attachment variations of this holster.
The nice thing about buying a Safariland holster is that the holster body can be attached to various platforms using either the included “UBL” belt mount for a duty belt or war belt, or via the QLS/MLS system of forks and adapter plates for attachment to drop rigs, belts, plate carriers, cars, etc.
The BLACKHAWK! SERPA holster is a level 2 holster, but I do not recommend it for any use at all. There are plenty of video’s showing its failure during gun grabs, rolling in the dirt, etc. Not to mention they do not allow the use of quality weapon lights such as the Surefire X300.
SPECIAL USE HOLTERS:
This is the category of other more "specialized" holsters like the Crye Gunclip. If you’re in the role that really needs to carry a Glock with Suppressor on it - i.e. a Direct Action type unit, go for it. For me, my mission does not need to conceal carry with a can on the pistol ready to use.