I know body type and clothing can dictate this, but what have you that carry an OWB mag pouch found to be the best?

I am probably going to order a JM Custom OWB 2 soon, and I would like a pouch or two as well. This will be for the range, carrying around the house/woods and possibly concealing in town on occasion.

The only thing I'll use is the old style Raven/Bravo style pouches with OWB wings. Shadow Holsters makes a great copy.

I use a Tulster OWB for my G43x and matching Echo mag pouch (I've added a kydex loop to hold a ThruNite Archer), and a nylon fishing shirt as a cover up

Versa carry has some water buffalo mag pouches that are over the top quality and prices that at times unbelievable in these times.

I use a kytex gear for 1911...rides high and tight...very nice.

https://kytexgear.com/product-category/pistol-mag-carriers/?doing_wp_cron=1653055482.4260179996490478515625

https://www.blueforcegear.com/double-pistol-belt-pouch.html

Most concealable.  Great retention.

I wouldn't say it's the most concealable, a pancake style is a bit more concealable, but it's a good pouch.  I liked the idea of being able to use it for different magazines so I picked one up last year before Christmas to try out and I've been using it almost constantly since.  My biggest gripe, and it's related more to the Shield magazine design and the fact there is no real spacing between the two openings, is that when using the eight round magazines with a spacer you have to stage them, i.e. I put the rear mag in first then put the front one in so that the spacer is resting on top of the rear mag.  Not that a big deal when changing mags since I'm going to grab the front one first, but it does bring me to the second quibble, you can't easily stick the mag you just removed back in the pouch quickly and easily since it's elastic.  It kind of messed with how I've been practicing my "administrative reload" for decades now since I was used to leather mag pouches that were easy to stick the mag back in but I've taken to dropping the empty/removed mag in my pocket now.  If I'm going back to that first mag for whatever is left in it I'm probably in a world of trouble and it's not going to make that much of a difference.

It is though, there's really nothing thinner out there.

Simple technique to get a mag in, start the opening with a finger, over the rounds in the mag, easy with practice.

Me, I NEVER put an empty, or even a partial, in a pouch.  Ever.  Those go in a pocket (or a dump pouch, but we're talking concealment gear).  But that's what I do, you do you.

I'd like to see a version made with belt loops on the ends, like a pancake style- maybe a leather back with an elastic front panel?  True, it's not going to be any flatter but it would have a smoother transition/profile.  Just personal preference.  

As for sticking mags back in the pouches, it's just a holdover from earlier training.  From the IPSC days of ejecting the mag and letting it fall to the ground to IDPA and retaining the mag, other training classes, practicing in different pants, etc.  Not ideal and requires a slightly different technique and generally not taught that way anymore, but when I carry my phone it's in my left pocket so I hadn't bothered to change up.  Cargo pants help but I don't always wear them and I don't normally wear a dump pouch, although I have to admit the Blue Force gear micro dump is pretty cool but I can't see any real everyday use for it. https://www.blueforcegear.com/dump-belt-pouch  I use a waxed cotton dump pouch in the woods (foraging) and a regular one (a Maxpedition) on my pistol belt.  As you said, different strokes, just practice with whatever you use.