Two colors meeting in a corner
Dividing in the middle of the wall will make the room look smaller. In my house, I painted the longer wall ajoining both rooms the color of the more dominant room, in my case it was the living room and dining room. The shared wall between them is the color of the living room. It looks great. The rooms share a wall, don't fight it, embrace it. Whichever room is the most open to view from the most common place, like a hallway, is the room I would choose to paint the shared wall that color. The other room will open up as a seperate room as you enter it.