I have G23 and for OWB Concealed Carry, I prefer the Blackhawk pancake holster. It hugs the body very tightly and has very low print-through. The only downside is - like all holsters with a thumb snap retention strap across the back of the weapon - the strap can get in the way when you present the gun. I've learned to work around the problem but it is something that a lot of people don't like about many holsters with retention schemes. There are many other CC OWB holsters and there are folks here who can tell you about them.
Also, there are many forum members who carry IWB and I'm sure they will chime in shortly on those holsters. For deep concealment you can't beat IWB but for me they are a bit uncomfortable.
Hope this helps but remember - there are as many opinions as there are holster brands and types.