The OER Dev Collaborative recomend the use of Creative Commons or otherwise openly licensed.
The primary licenses for open educational resources are CC BY and CC BY-SA. These licenses drive innovation and creativity, including commercial reuse. Furthermore, these licenses strongly support the overall GDL goal of sharing, translation, and contextualization of educational materials, open textbooks and open educational resources.
We are collaborating with several content platforms who are addressing the increasing public demand for sharing under CC licenses. We encourage all projects developing content to visit creativecommons.org for more information.
Creative Commons has developed a cc toolkit for user-generated content platforms. This toolkit covers the elements for a basic Creative Commons platform integration, including aligning legal terms to CC tools: installing the CC license chooser, displaying CC licensed content with the correct logos and links and how to communicate CC to your users.