If I was going to build a shower, I'd consider using Kerdipanel on the walls and building the pan with Kerdi as well. If you aren't familiar with this shower system, there are some videos, installation guides, etc., at www.schluter.com. A conventional shower uses an embedded liner in the pan leaving about an inch of porous deck mud on top. The tile and grout will leak some water through, and it will get into the setting bed, and the excess will drain through the weep holes of the drain. A surface membrane shower is different...the entire surface is waterproof to the drain, so the walls and floor never get wet. In a high humidity area, where drying can take a long time, a surface membrane waterproofing system has distinct advantages in keeping mildew down.
If you wish to build a conventional shower, it doesn't really matter which you use, Durock or Hardiebacker. My limited experience is that the Hardie is less prone to crack if you get a screw too close to the edge. It may be a little harder to cut cleanly, though. In either case, ensure you install a vapor barrier behind it, lapping over the pan liner and do not screw the bottom in which will compromise the liner. Put the cbu up before you install the setting bed, and that will lock the bottom edges in against the studs rather than screws.
For good help on tiling issues, check out www.johnbridge.com.