What is the most concealable holster that is also user friendly for a Glock 23?

There are lots of good holsters. Some of the best are made by Blackhawk. Others are made by Eagle Industries. You can try www.botachtactical.com for more. Remember that the holster needs to conceal the weapon based on the clothing you are wearing. You also want to be able to get to the weapon fast, so an ankle holster is not a good option.