[LukeShu]

Any recommendation of a "default" license to use if you don't care too much about licensing will always carry strong opinions of whoever is recommending it. So, instead, here's a decision tree of good recommendations based on the two biggest decisions that factor in to choosing a license:

                          start
                            |
                            V
           if I modify it, and give someone a
          compiled binary of that, should I also
         have to give (or offer) them the source?
                       |        |
                   yes |        | no
                       |        V
                       |      MIT/X11 license
                       |     (alternatively,
                       |      Apache 2.0, or
                       |      2- or 3-clause BSD)
                       V
                is it a library
                 or a program?
                   /      \
          library /        `----, program
                 V               \
    can it be used by programs    \
     that DON'T give/offer the     \
       source with binaries?        \
           |         \               \
       yes |          \ no            V
           V           `-----------> GNU GPL
        GNU LGPL                    (alternatively, GNU AGPL)

Whether or not you think the "default" choice to each question should be "yes" or "no" is something that people argue about plenty; whichever you choose, someone will tell you you chose wrong.

As for the "alternatives" in parenthesis at the leaves of the chart: if you don't care about licenses, the default is probably fine, but if someone told you that you should use one of the alternatives at that leaf, I wouldn't argue. (Apache 2.0 comes in over MIT if you care about patents, AGPL comes in over GPL if you care about SaaSS)

[e12e]

It's a good chart, but I'd add: is the source code meant to be an example/educational and/or is trivial[1]: cc0 - somewhere on the top right.

[1] by definition trivial code isn't copyrightable - but "trivial" is subjective. If you, as the author feel it is, might as well clearly signal that and use cc0.