When comparing GPLv3 vs WTFPL, the Slant community recommends GPLv3 for most people. In the question“What are the best open-source licenses?” GPLv3 is ranked 4th while WTFPL is ranked 9th. The most important reason people chose GPLv3 is:
Requires people building on your work to licence it for others to use.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Copyleft
Requires people building on your work to licence it for others to use.
Pro Ensures that the software does not become proprietary
Pro No disclaimer
It does not explicitly disclaim implied warranties which some rather idiotic legislations appear to follow.
Cons
Con Limits the developer's ability to package or use other libraries/software
Con Copyright
Requires people building on your work to license it the same way you did. Good if you want to pull their code into your project, but issues for potential end users can arise.
Con Ensures that the software does not become proprietary
Con Not fully proven to be valid
It has been used in many open source projects, but is not fully validated, although widely accepted as an open source license.
i.e. Proven in a court of law.