The Steerage, Stieglitz.
The relative tidiness of the framing above contrasts with the relative untidiness below, arguably echoing in the composition the contrast between the two classes of people involved, although this might be a bit of a stretch.
As a composition, I think this one is fair rule-following, as far as the simple rules of composition we run in to over and over. It is a particularly fortuitous arrangement of shapes and lines, a little random to be formal as such, but while it's loose I think it's pretty obedient to convention.
Of course the point of this image is, as is so often with the really good ones, essentially political.