Comparison of different forms for the "spin" and "orbital" components of the angular momentum of light

We compare three attempts that have been made to decompose the angular momentum of the electromagnetic field into components of an orbital and spin nature. All three expressions are different, and there seems to be no reason to prefer one to another. It appears, on the basis of classical electrodynamics, that there is no unique way of decomposing the angular momentum of the electromagnetic field into orbital and spin components, even in a fixed inertial frame