I have grown to really like the MPLv2. It gives the protections of GPL for the code you actually wrote (changes need to be released) while still allowing closed

I have grown to really like the MPLv2. It gives the protections of GPL for the code you actually wrote (changes need to be released) while still allowing closed source software to use your code as a library (it doesn't require releasing files not included in your code). This means that a wider range of people/projects are likely to use your code, but any bugfixes or in-file features need to be open sourced. This results in a higher quality of code, more complete and rounded libraries, and not everybody's kitchen sink gets sent upstream for potential merging.