As a library writer, the most important question is very simple: do you want to allow others to distribute proprietary applications build with your library? An

As a library writer, the most important question is very simple: do you want to allow others to distribute proprietary applications build with your library? Answering this question may be very difficult, but once you do, the choice is simple: If you want to allow, you probably want a permissive licence. If not, you probably want a copyleft licence (I'd suggest GPLv3).