Wood or wood planks usually run the length of a room. Most of the time, they run the length of a hall..... your dilemma.
Sometimes it's best to use the directions that you normally use to walk into a room as a guide. If the living room will always have a rug covering a large part of the floor, that can influence your decision.
In the lower part of the drawing, it looks like maybe the dining room area? If so, that would have a table and chairs, once again breaking up the visual length of the room.
If the doorway on the right is the kitchen, you would often walk from that doorway, through the dining room then down the hall. In that scenario, the planks going up and down the hall might be better.
It's a tough call.
If you already have the material, you could open up a couple boxes and lay a bunch of pieces on the floor to get a real vision of how they will look. Don't lock them together, just lay them side by side
Try it one way, then the other.