I carry exclusively OWB and have found, if clothing choices abound, that you can conceal most anything. In that regard, I gave up tucked in shirts decades ago. So here a some choices.
In a large caliber, I like an Officer's Model type 1911 with an alloy frame of course. I've had no trouble concealing the straight grip model vs. the bob-tail. My Sig RCS in .45 does well in this regard, and still carries the traditional 7+1 load out.
For medium calibers, my choice has been either a S&W M36 or a M60, either with the 3" bbl. and adj. sights. Neither is a problem to conceal and does not print even when carried under a fairly close fitting t-shirt. Both guns have round butts, one with fitted wood stocks the other with Smith's compac grips.
For really small carry, where bulk is not wanted, my current choice is a Sig 365...in use it's invisible, plus you get the advantage of superb sights & accuracy, as well as increased capacity; but must settle for a 9mm load choice. Day to day, this is usually on my hip when I leave the house for town. At 20 oz., loaded, it's no drag on the belt.
Lastly, if I have to pocket carry, I have a S&W Bodyguard380 that will disappear nicely in a shirt pocket! It's not much, but it's better than a sharp stick.
As to holsters: I like and make an open top, tightly fitted version of the old Tom Threepersons design. The attributes are: minimal bulk, lined to protect the gun and to ease the draw stroke, and generally in black to minimize recognition if my shirt rides up. It rides high on the belt, and allows good access when worn at 3:00. Farther back, hinders access when seated.
Pic below: Sig P365 in high ride holster in usual position. Doesn't take much shirt overhang to hide.
HTH's and YMMv, Rod