I think I prefer the `galsim.wcs.readFromFitsHeader(header)`... More now after seeing both written out than I did thinking about it in the abstract when I raised the question!

My rationale is
* Many of the users may hope not to need to know about the base classes etc. that underly the GalSim WCS code, and the additional CamelCase of the BaseWCS in the latter call forces them to confront it.
* Even deeper than that, it's also a fact that a number of (even Python-using) astronomer prefers to try and get away without thinking about OOP as much as humanly possible, and the former syntax allows them to do that most straightforwardly.
* If I were using GalSim for the first time and exploring it, for which I would be using `ipython` and the tab completion to negotiate the `galsim` packages, classes and methods, I would have found the former case *way* faster!