Great post idaho.
My two major "types" are basically range and concealed.
For range work I just use a Blade Tech belt holster with a straight drop. Really any decent kydex, 0 retention, gamer rig is fine for that. I don't go into gun golf enough to make the differences in the IDPA and USPSA holsters matter enough. I just look for something that doesn't both chew up my belts and draws ok. This is not an outside the waistband concealment holster, just whatever their "gamer"/range package holster was when I bought it. It came with a double mag pouch as well.
I also have a Comp-tac double mag pouch that I can use for games/range practice/classes. It is actually quite a bit faster to work from because not only does it not tuck the mags into my side, it cants them away. Of course that makes it even worse for concealment.
Clothes/dress requirements matter here the most. I am a small guy, and I don't have any type of credential other than a carry permit. So if anyone who is apt to get overly excited at the sight of a holstered firearm makes me, I can expect a larger helping of grief than someone who can say "It's ok, I'm a cop."
Tucked in shirt carry
I use an Alabama Holster Company pocket holster. It does a good job of keeping the gun stable in the pocket and an ok job of breaking up the gun's outline. Being fitted kydex it does an admirable job of keeping lint out of the gun. What I like about the design is there is both an aggressive "hook" to catch on the draw AND a thumb tab to break the retention of the holster.
There are a lot of designs that feature either a hook or a friction material to catch on the pocket and a couple that have a manual tab, but after using the Alabama design I think getting both is the right answer. Between the two I have never had the holster fail to get disengaged during the draw. Using the thumb tab or the hook primarily sort of changes depending on exact pocket depth, size, and the cut of the pants but this is the best solution I have found for pocket carry.
I also have a couple of "tuckable" holsters. Of those the Comp-tac M-tac is still a serviceable choice for behind the hip carry. It does an ok job at concealment and a great job at being comfortable. The issue for me is a tucked in shirt really slows down the draw to the point where getting a hand into a pocket and wrenching something out of it is just as fast, or faster. Yes, even seated. Neither is great for "in fight" access. End result is my M-tac has been moved to being primarily a bedside/drawer loaded gun "trigger guard cover". It is great at this as the leather backing can act as a thumb break and we had the conversation about Glocks not having safeties.
Untucked T-shirt Size that mostly fits
I have a Small Gun Holster from Darkstar Gear that does yeoman's work in this role. It is comfortable, secure, and because it anchors with a "Pull the Dot" style Blade Tac loop also manages to be "easy(ish) on off" while not coming loose when pressure testing/rolling. Tom at Darkstar makes this design for many of the small, single stack autos and the Smith J-frames and Ruger LCR's. To be honest I like this holster so much I would check to make sure I could get one before picking a "not a real gun" size gun.
It is an appendix/felony carry holster. As a bonus the holster is non-bulky enough that the entire holster and handgun can get jammed into a pocket enough to stay there. That is a factor for the "I have a handgun and I have to use a public rest room" question that some folks fail spectacularly be dropping and grabbing for loaded handguns, or leaving a gun in the can.
Untucked Loose T-shirt on up to Gun Burka/Whatever the tactical name is for an untucked button up shirt. Either flannel or one of those Columbia ones
Current answer here is a Darkstar Gear Appendix Inside the Waist Band holster for a Glock. It works pretty damn well. In an XL T-shirt I can hide a Glock 26 just fine. If I go full Slob/Burka I can carry a 19.
No issues with durability or retention, and there is a decent amount of adjustibility with regards to ride height and even a possibility of a bit of cant/angling so if you are having trouble finding your carry sweet spot this holster is very forgiving. This holster is also adjustable for amount of friction/retention and I have mine cranked up a bet.
Both my Darkstar Gear holsters have full sweat guards as I have come to prefer those quite a bit. They shield my skin or undershirt from getting cut the hell up from my rear sights. Yeah, laugh all you want. I know, warrior through it, but fucking Warren and Trijicon seem like they are in a war to see who can get the stabbiest rear sight angles onto a sight set. I also like that I can use the sweat guard to lever the holster body such that the barrel can point away from me the whole time I am holstering.
The only modification I have made to the two holsters is to use some adhesive velcro from Hobby Lobby to attach a Dr. Scholls Gel Heel Wedge to the backe/barrel aspect of the holster. This cushions the hard kydex and gives a bit of a wedge to help tuck the butt of the gun further into my body. Being able to move the pad around is a help because the exact "right" spot can vary a bit depending on clothing, or just how fat and bloated I feel. Again, stop snickering. Yes, I have a fat holster/gun combo. It is when I have to resort to the fitted t-shirt gun with larger shirts. Stop judging.
I have a Raven Concealment Vanguard 2 that does everything they say it will. It is minimalist and tuckable. It is also more secure than I think it should be. It has never let go of the gun when I didn't want it to, but the "only over the trigger guard" design still gives me pause for serious use. That said it is reversable so I recommend everyone with a Glock buys one and sets it up for support side carry in case they get one or more fingers on there dominant hand dislocated and go months trying to rehab ROM and strength back into it.
I have a bullhide belt from The Beltman that is awesome. Unfortunately I am told his customer service has gone south so I can't really recommend using him as strongly as I used to.
Wilderness Tactical Instructors Belt- I love this fucking thing. It is infinitely adjustable, which matters a lot more when various holsters/guns have to interact with various pants on various days. I have the 5 stitch without the liner. It is plenty rigid. Buy with confidence.
Fuck Off Tools
I have an ESEE Izula in a Darkstar gear horizontal belt sheath on pretty much anytime I don't have to tuck in my shirt. The small blade carried centerline(ish) journey got started for me based on an old member of this forum, DevilDogJim. He recommended/used a Clinch Pick which sent me on a search to find one and try it out. I have a real Clinch Pick and Trainer and am both sold on the concept and design of the knife. However my reading of PA's knife laws seems to indicate that trying to explain "lawful self defense" as "valid use" is a "beat the rap, but never the ride" matter in PA so a purpose belt weapon is less attractive to me than a great utility knife.
My Izula sees plenty of utility use, my Clinch pick was nearly as big a uni-tasker as a firearm.
When I was carrying revolvers I was guilty of tucking speed strips into pockets. Sometimes I would carry speed loaders, again in pockets.
I still end up pocketing a spare mag for my Kahr occasionally depending on what I am wearing. If I have an untucked shirt though I am using Kytex mag carriers for both Glock and Kahr magazines. These are not competition style carriers and they do a good job of tucking the mag into my body.
I carry a small flashlight in a pocket where I can reach it with my support side hand. Currently I have a StreamLight Pro-Tac 2L which uses lithium batteries and has 200 lumen and 80 lumen modes. I like mine just fine, and got a good deal on it.
If I were buying again I might pick the version that takes AA batteries instead though. It is a little weaker, but I would be free of the fire/explosion concerns associated with lithium cells of different charges. I would damn sure not use rechargeable lithium batteries unless I were more dialed in than I am. I carry the fucking thing in my front pocket most of the time. I have accidently turned it on and my first sign that it had been running its 200 lumen beam was a "Why the hell do my boxer shorts feel like a sauna?" feeling. Fuck a fire in that scenario.
Anyway. If I could only pick one thing from the above list it would be the flashlight. It gets used constantly and has solved plenty of "need to see better" problems, and being able to light up a corner may have kept me out of needing some of the other gear on a couple of occasions.
Train Hard, Stay Safe.