I've used several things in the past but have decided that I like peat moss over any of them. It retains moisture easily, is cheap, and is easy to clean out. Most on TFO seem to use a combination of peat moss and cypress mulch, or cypress mulch exclusively. In the end, it's your decision. I encourage you to find what's the best for you, and let us know what it is!
For hatchlings I use a combination of all the above. I have a small dry portion of the tank of hay (about 1/3), that is seperated by a wood block from 2/3 cypress mulch. Sitting on top of the cypress mulch I have an upside down shoe box with the lid on filled with peat moss for a humid hide. The hide is kept damp, cypress mulch is sprayed daily and the hay is kept dry. The hay molds easily if wet so the areas closest to the hay I don't spray.
BTW, what are you feeding your torts in that picture? Looks like tortoise salsa!