It seems equivalent to talk about combining left and right circular polarization vs combining two plane polarizations for a monochromatic light beam. But I don't understand how that converts to talking about single photons (or whether that makes sense either, haven't learned any quantum mechanics). Is one of the two preferred or a fundamental property? If so why?
Intuitively it makes sense to first understand linear polarization, as it describes wiggling of the E-field in one dimension. Circular polarization describes an E-field that's direction spins in a circle (two dimensions).
There's nothing wrong with keeping a photon's polarization in terms of left-circular and right-circular light and it can be made completely equivalent to linear light - but for the sake of understanding, it's smarter to learn and understand linear light first since it's simpler to understand and certainly not less fundamental).