Personally, I like CC BY-SA better than the GFDL.
There's one thing I want to point out, though: a lot of people seem to completely ignore the exact license and only mention that something is under "a Creative Commons license", which is incredibly vague. Only two of the Creative Commons licenses are free and therefore good for manuals. One thing I worry about is people who hear that "Creative Commons licenses" are good deciding to use the nonfree licenses and thinking they're doing just as good as those who use the free licenses.
