i like a balance... heavily planted mid to back portion, then a more open front, for 2 reasons, 1 it forces the fish to the front of the tank ( better for viewing ) when they arent hiding, it gives them a open area to swim when they wish....
I prefer to give my fish plenty of plants to hide amongst if they need to. Which, with a 4yo running about and staring into the tank from time to time, they do like to hide.
I also like to create veiwable places for my pleco to hide (under a bit of slate) it took him 3 months to overcome his shyness and I often wondered if he was still alive! So this lets me see him without disturbing him.
My big tank is goin to have some heavily planted areas and some caves and some wood. I think the fish would get stressed if they could not hide.
But then you do get the bigger fish who rip the plants out..