Don Hume's PCCH (Preferred Concealed Carry Holster) is the most comfortable one I've ever used. Made from thin but firm leather, has a body shield to protect my "hide", and conceals very well. I have one for my G19 and I'm wearing a Colt Combat Commander in one right now.
I can wear either of these in the PCCH all week long with no discomfort.
I have a CompTac CTAC and it's an outstanding holster, I wear it mostly when teaching as it's a super easy one to reholster with one hand but I have enough "waist" where if I try to wear it all day, it "digs" a bit.
The Don Hume Open Top with metal clip are very good quality and very affordable but the PCCH is more than well worth the price difference.