I have a Serpa for a Glock (not the 19) and it's okay, but I only have it because I got a smoking deal on it - no package, missing the paddle, Glock 20 size, brand new, $20 iirc.
So okay, fine for cheap. But I have no specific love for the holster. I would probably look elsewhere if I was paying anything like retail pricing.
I am TOLD (no personal experience) that the Comp-Tacs are nice, as are the Ravens. I am sort of eyeballing a Raven myself, but I can't comment on them from personal experience. They are recommended to me by people with more experience than I have, that's all I can say about that.