I'm tiling my shower up to about 7' and the rest of the shower and ceiling will simply be painted. What material should I use on those?
I am using RedGard as my waterproofing method so there will not be any waterproofing BEHIND the backer board.
You don't have to use a backerboard on shower ceilings - especially if you aren't tiling it. You can drywall it.
If you do use a backer board I would suggest Hardieboard. You would then just put a skim coat of joint compound (mud) over and sand.