Disk Method is the most accurate method and probably the easiest to teach a class, but can be tedious given a long list of numbers.
Washer Method is easy to teach kids, quick with large lists, does not require carrying over or regrouping. It’s too difficult for small lists of arbitrary numbers.
Shell Method is tedious for larger lists than about 15-20 numbers and has no meaning when used on arbitrarily generated questions . In addition – it relies on recoding which assumes that there are no changes in units or operations between selections of digits to make an easier/harder calculation.