Cinder block or concrete for shed basement?
You do have a 3rd option, ICF forms or blocks. These are assembled like children's building blocks. Rebar can be set in the horizontal braces then filled with concrete. One advantage is they insulate the wall (I think it is close to R50). The last below grade shop I built was 11' with these and no forms to strip. The walls never leaked like block walls do so that was another big plus in my book.