IIRC
The 'A' is for american market,
'C' for chinese market,
'E' for european
and 'G' for global.
they seem to be priced more or less the same, a couple of dollars difference.
From what I have seen and worked with it, its fairly straightforward to setup and use. I was really hoping to leverage the NB-IOT features but its still in a nascent stage of deployment here..