Portrait v Landscape
Scenes with a strong vertical component clearly lend themselves to a vertical orientation, and vis versa. Whilst the sequence of images shows some subjects best suit a certain orientation, not every subject is so clearly pigeonholed.
I found the focal length of the lens also influenced the choice of orientation. The natural curves of the block of flats worked well with a wide angle lens and a horizontal orientation, although a telephoto lens from the same position would perhaps indicate a vertical orientation.