Any of the Creative Commons licenses are established, legally-compliant tools for sharing one’s work broadly while still retaining copyright ownership. The most generous CC license is the CC-BY because any kind of re-use is permitted, as long as the author receives attribution for her work. The CC-BY-NC license is a bit more restrictive because it prohibits the party reusing the author’s work from making money from it. If a party does use the author's work for a commercial purpose, the license is automatically revoked and the original author can thus sue for copyright infringement.
Which license to use is really a matter of individual preference. Overall the Library recommends CC-BY to allow all reuses (even commercial ones can benefit research and researchers). But the author is absolutely encouraged to use whichever license s/he is most comfortable with.
