In a completely walled property, which wall should I plant sunflowers against?

The four walls are more or less NESW, 2m high. Northern hemisphere where will sunflowers do the best?

I would say the north wall, facing south, as long as they are watered well. Mine always grow excellently in full sun. I have some on an west-facing wall and they do bloom but they are much shorter, at least by half, only getting afternoon sun.