belts make a big difference. I have been carrying Glock for....well a very long time, on a daily basis. I have gone through HUNDREDS of holsters, There is a few 25 gallon rubbermaid bins in my shop just full of them.
That said the absolute number one in my mind is Mike P (defensiveholsters.com). I have never found a single thing to complain about with it and I wear it about 18 hours a day (sadly, i don't sleep much).