Like many of the others, I also believe that holster-fit is a very individual-preference issue: the way the gun, the holster, and the person's body anatomy and chosen dress interacts is unique to each individual.
With that said, here's what I've found to fit me:
99% of the time, my carry-gun is my XDm9 3.8 Compact. 99% of that time, it's in a Pure Kustom Black Ops Pro, IWB on my strong side (3-o'clock). This is my most comfortable IWB with this gun, and I really only switch to either a Comp-Tac Minotaur MTAC (standard cant) or a CrossBreed SuperTuck when I have specific concealment concerns, which typically arise only if I step away from my usual jeans-and-an-un-tucked-T-shirt dress routine.
If I can't get the XDm's profile slim enough with the above, I'll switch down to my alternate, a Kahr PM9. 99% of the time when I'm carrying that pistol, it conceals more than well enough with my Garrett Silent Thunder Slim II. I can further suppress its profile if I moved towards using either a Desantis Nemesis or a D.M.Bullard pocket holster, but I try to keep from going this far, as it moves the pistol out of my most-trained-for access.
I really do try to keep my carry consistent - all of my IWB holsters are set up for approximately the same cant, same carry position. 99% of the time, if you patted me down, what comes out will be my XDm9 3.8 Compact.
I completed a one-day "intermediate" level pistolcraft course using my primary carry, holstered in the Pure Kustom (riding on a standard Beltman dual-layer bullhide belt), the rig was perfect, and came through the sweaty and hot day looking not the worse for wear. We also practiced one-handed malfunction drills in this class, and I repeatedly indexed this IWB holster as my hard-point for various functions: the holster never collapsed.