I've been carrying a Glock 19 in a Milt Sparks Executive's Companion IWB leather holster, positioned about 4 o'clock, for over a decade and I've been very pleased with this setup.
All my IWB holsters are the Milt Sparks Executive's Companion. I also carry, depending on the situation, a Glock 27 and a Kahr PM-9 but the Glock 19 is my primary carry gun.