I carry a gen4 G19 every day AIWB, when I'm not at work. It's small and light enough to conceal easily without unnecessary discomfort, but still holds 16 rounds. I pop a happy stick in it on the nightstand, for 34 rounds before a reload.
I found the larger grip of the 19 is faster out of the holster than the little 26/27 also, without giving up any concealment in normal clothing. If I wore a suit (I don't), I'd chose the 26 though.
I do occasionally carry my G20 or 21 concealed, and it's not too bad, but certainly less comfortable, and a bit slower in a reactive situation.
Part of the comfort issue is just carrying every day and getting used to it though.