The Bianchi Professional 100 is a versatile IWB holster that I use for everything that I carry. Size 11 fits all the classic SIGs and Size 14 fits all of my 1911s.
I never knew how deadly holsters are until I started paying attention to the P320 "discharge" threads. Now I strive to choose a holster that won't shoot me. Seriously, I still carry revolvers so you know right off the bat that nothing I have to say is of value.
IWB is my primary set up. I always choose a holster that I can move around IWB for comfort while seated. Something that can slide a few inches makes a big difference when you're being poked by something sharp.
My OWB holsters range from carved and tooled leather BBQ holsters to the dreaded and presumed deadly SERPA retention holsters.
I've come to accept that holsters are something intensely personal. What works for me may not be something another person could live with. I have a lot of discards that for one reason or another wasn't just right for me. They probably looked good or were highly recommended but just didn't pan out. A year from now I may find that this discarded holster works for a different pistol.
The only time I buy a BRAND NEW holster is when I've tried it with a used eBay holster at less than half the cost of a BRAND NEW mistake. That's a tip you can take to the bank. Buying holsters is expensive and you can expect to make some mistakes. The Bianchi Professional 100 is the most versatile holster that I can recommend for IWB carry.