Cement board is a lot easier, I can't think of a reason not to use it. Any old mud jobs that I have demolished from old houses had heavy metal laff (sp?) nailed to the studs and then mortar troweled right to it. You may want to use a membrane or tar paper behind it. I'm not an expert so I don't know everything about it - I only know that all wall mud jobs I have seen use this laff.