Tim,
Good question. I am going to throw out there that I suspect (but don’t authoritatively know) that a relatively large cell soft
wood would be best for moisture absorption. If it were me, I would go with relatively new soft wood sawdust for moisture absorption and some cedar for odor control.
Now if for some reason you can’t find softwood chips I certainly would not turn down hard wood chips. I also expect that the softwood will break down faster so it might be returnable to a garden sooner.
I am not certain how long or exactly what steps one needs to take to make humanure safe for human use, but I would be tempted to let this age and then apply to something like maybe some
trees or other woody stock. My thinking is that nasties like ecoli are transmitted to edible crops not by growing through the
roots and into the plant tissue, but rather gets splashed or otherwise applied to to the leaves from some sort of direct soil contact.
Anyhow, these are just my thoughts and take or leave them as you like.
Eric