I cannot comment on the gen 4. So i will state only how i feel about the gen. 3 models 17/19.
I like the ergos, the trigger, the simplicity, love the reliability, and appreciate the durability of the gen. 3. I shoot the gen. 3 Glock models better than any other autos that I own, have owned, or have fired previously. A gen 4 probably cannot offer me anything of real worth that I am not already getting from the gen 3. That is just me.
Now, if the gen. 3 doesn't not fit you as well as the gen. 4, then give the current models a little time to work the bugs out (if there are any to work out) and get a gen. 4.
Handgun quality and preference is percieved as many different ways as there are people to percieve them. Research, pick em up, shoot em, buy quality, buy what fits you, and go on with it.
Good luck to you sir.