Emerald, Ruby, Sapphire are my pick. Yes, there region might not look so beautiful today, but imagine what a remake could do. Beautiful towns and clever design, like sootopolis city, where you have to dive to reach it, and pacifidlog town floating on water, fortree City; it's made out of tree houses! As well as many other great locations like Mt Pyre, Meteor Falls, Abandoned Ship, Seafloor Cavern! Aswell as awesome backstory to the legendaries! I <3 it!