Getting back into the firearm game after several years. I am not sure whats new or whats popular these days. I sent my Glock 19 Gen 4 slide off to be milled for a Trijicon RMR and that month long lead time has finally come to an end, and I just realized I dont have a holster for the newly equipped gun. I was using a Crossbreed Super Tuck before, but that platform is probably dated at this point.

What would you all recommend, or what are you all using?

If you can carry appendix, any of the reputable kydex companies are good (Trex, Tier1Concealed etc). I have a Trex sidecar and have used them for about 5 years. I carry a 19.4 with an x300u. All of their holsters are cut for optics. I wore the first one out (kydex stretched and couldn’t tighten it anymore) about 8 months ago and they replaced it for free. But Lucas is kind of weird so I understand the hate for them

I had an appendix holster years ago. One thing I remember was something simple like taking a piss in public became an affair. I don’t recall what driving a car or bending over was like. I also don’t recall what riding was like with such a setup. What’s your own experience with that? Another thing is, being a mechanic I have to often carry large/heavy things, which would result in hanging up on the gun or painfully pushing it into my stomach.

I know this one is pricey, but totally worth it.
There's a drop down menu for RMR cut.
There's a suede type material on the outside that makes it stay right wear you put it.
It's a buy once, cry once type holster.
https://www.tacticalholsters.com/product/incog-eclipse/

I just purchased a side car from the EE. This holster looks interesting. I’m checking reviews right now.

There are setbacks, but I think the pros outweigh the cons. I crouch instead of bending at the hips. Better for the back anyway. Carrying items in front of you often would create a problem. You’ll probably be better served with some type of 4 o’clock hybrid holster. I prefer appendix 98% of the time, but I have other holsters for certain scenarios.

I got a side car on the way. The other gentleman above recommended a kidney holster. Might purchase that as well. Anyone else like the incog?

I ended up ordering the incog just now. Hope it pans out well, it looks solid. Cheers to both of you.

Cool!
At least you have options. haha
The belt clip on the incog keeps it nice and tight to the body, I like mine a lot!

Yeah work and play provide a variety of awkward firearm predicaments. Should be good to have both.

I have 2 Vedder Holsters  that get carried regularly. Just the Lighttuck.
Had trouble with one getting too much slop in it, sent it back, and they gave me a new one.

NSR Tactical with a The Wilderness Instructor belt 5 Stitch or CSM in 1.5 or 1.75 inch width

Tulster OATH for my g19 w/RMR

My number one suggestion would be to get a JM Kydex AIWB with an RMR cut and for a 17 length (yes, not 19). Get it with the large foam wedge that can be taken off and on so its comfortable for both hip and appendix.  The AIWB is my favorite holster I've ever owned.  Amazing quality and design.  

https://www.jmcustomkydex.com/p/AIWB.html

Regarding comfort with appendix carry.  It is a system where components cannot be overlooked. I'm convinced many that have tried appendix and didn't like it didn't have the right equipment/and or didn't know how to set it all up properly for their body.  Spencer Keepers offers a class on just carrying appendix and its amazing how much you can learn just about this carry position.  

1. Starting with a truly proper AIWB holster.  I'd say 95% of holsters marketed for such are not close to correct.  The right holster design conceals better and is more comfortable. It must have a vertical wedge and a horizontal cam.  
2.  Proper belt like an EDC Foundation.  Not too stiff but properly mates with the horizontal cam on the holster.  AND the buckle must be minimalist or it will protrude with a gun in this position.  The EDC has the perfect buckle.  
3.  Boxers or compression underwear go a long way for comfort.  I use Underarmour compression underwear and compression undershirt.  These are a huge part of comfort  because they make the pistol slide against the material, not dig and stick to your leg/belly.  

Another great company is Tenicor.  Their Velo 4 holster is a brilliant design for appendix which I also own. Their Certum is designed to work well for both appendix and hip.  Plus - these automatically come cut for an RMR.  All of Jeff Mau's gear is pressure tested in legit force on force training.  He's really serious about innovative gear that works.  

Good luck!