YYYY/MM/DD is the best format(edit: it's the same one used in article ofc), since it is also sort-able
I like YYYY-MM-DD as it is also sortable and doesn't require any escaping as a file name on windows or Linux. It's part of ISO8601.
slashes or dashes makes no difference to me, still the most readable formats, since we are used to the biggest number first, from our numbering system :)