I think the mere fact there are licenses involved is the best indication that what we perceive to be 'free' (as in 'freedom') and 'open source' is never actually going to be free. That there are four, distinctly different Creative Commons Licenses is evidence of that.
When it comes down to outright simplicity of understanding, WTFPL is likely leading the pack. But I do think Richard Stallman offers the best definition of what free software needs to be. Freedoms 0 - 3 should be all that is required. Anything else starts looking like restrictions, which means freedom is no longer on the table.