So I want to 'protect' my userscripts with a license. But there are so many with little differences.

I was wondering what license you have chosen and why...

If it's something I really care about and want others to share their modifications, I use GPL. For libraries I use LGPL so others can use it with their non-GPL code, but still have to share any modifications made to the library itself. When all I want is attribution, I use MIT. And when I really don't care what happens to my code I release it into the public domain.

Hence, this is why I released my code for OUJS under the GPL from the start. It is forever GPL. No one can pull a US.o and make it closed source, which is possible with MIT and several other open source licenses.