We have around 200 Gen4 9mm Glocks and have had a lot of issues. I do believe they are corrected now with the new ejector I put in them, though. Since I switched them out I haven't seen nearly as many malfunctions at the range as I was before.
The Gen3 22s we had earlier would place a pile of brass in a six inch circle if you were shooting at a target standing still. Our Gen4 9mm are almost as consistent now.
If I were to go out asnd buy a handgun for myself today, it would be a Gen3 9mm.