It is not possible to recommend a specific license, you should always choose the one that best suits your interests, which may be different for each document. In our guide on Open Science you have an explanation of Creative Commons licenses.
The recommendation is to always choose the most restrictive license that meets your interests, so it is easier to give a more open license later. If you license a document and then change it, people who have downloaded the work with a more restrictive license will not be affected by your change. In fact, it is always recommended to include the license within the document itself, just as you do with copyright.
