I run gen 4 now, have been shooting G19s for a long time. I like the larger mag release, texture, and dual recoil springs. When the M models hit the civilian market, Ill go to those due to no finger grooves. My 17 gen1 is my favorite, but its a gen1, so it doesn't get used much. Don't get an RTF2 model if you plan on Conceal Carry with it, unless you just want to have no skin where it touches
My only G19 right now is a Gen 2. I prefer no ribs. I've got a G26 3rd Gen because it's more carry friendly and takes all 9mm Glock mags and grip extensions.