IWB: Well, apparently 18 degrees is most comfortable, in my case, for behind-the-hip IWB, because the Milt Sparks VM II is built that way, according to Tony Kanaley, who now runs Milt Sparks. I do not like that draw angle, but, for traditional behind-the-hip IWB to be tolerable, 18 degrees, it is. Notably, this severe amount of cant seems less-evil with shorter-barreled handguns, as they “clear leather” more expediently.
For shorter-term IWB carry, like two to three hours, max, I would rather carry nearer the point of the hip, with ~5 degrees of cant, something I will do with a sizable revolver, when I am in an environment* where I want serious shoot-ablity, at longer range, but just have to carry inside the trousers, due to cover garment length.
OWB: I “prefer” zero cant, at ~0300/0900, ideally. 0300 is where I carried duty handguns, for almost 34 years, which does tend to hard-wire one’s conditioned reflexes. (My mandated/issued duty holsters had some amount of cant, which I did NOT favor.) Zero cant remains OK a bit forward of 0300/0900, but just a bit of reverse cant makes for a cleaner draw, forward of the hip. An example is the slight reverse cant seen with the Kramer Crossdraw version of his Vertical Scabbard, which I will wear a bit forward of my hip, for a “strong-side” draw. (Wearing a sizable revolver forward of the hip is not the most-concealable set-up!) The practicalities of concealment often mandate carrying a bit farther back than 0300, with whatever cant is built into the Milt Sparks PMK, my most-favored revolver holster. The slightly lower position works better for me, requiring less shoulder/elbow/wrist articulation.
For reference, I have a short waist, and relatively long arms, so carry far behind the hip makes for somewhat severe articulation of the wrist, elbow, and shoulder joints, during the draw, especially if using IWB carry, and especially if carrying on my right side.
*An example is when I drive an elderly neighbor/friend to her bank. I am age 60, and getting a bit stooped, and she is in her late Eighties; we may look like easy prey, to the “follow-home” robbery types.