Always choose WHATWG over W3C, no exceptions.
Anne van Kesteren, (a WHATWG member who was a major contributor to the the HTML specification prior to the WHATWG and W3C versions diverging, and who remains a major contributor to the WHATWG specification) describes the current situation between WHATWG and W3C as follows on his blog:
The W3C has forked the [WHATWG] HTML Standard for the nth time. As always, it is pretty disastrous:
- Erased all Git history of the document.
- Did not document how they transformed the document. Issues of mismatches have already been reported and it will likely be a long time, if ever, before all bugs due to this process are uncovered, since it was not open.
- Did not discuss plans with the wider community.
- Did not discuss plans with the folks they were forking from.
- Did not even discuss plans with the members of the W3C Web Platform Working Group.
- Erased the acknowledgments section.
- Erased the copyright and licensing information and replaced it with their own.
2019: The war is finally over
On May 28th, 2019, W3C and the WHATWG have signed a agreement to collaborate on a single, authoritative version of the HTML and DOM specifications.
According to W3C’s statement, the two parties have come to the following terms:
- W3C and WHATWG work together on HTML and DOM, in the WHATWG repositories, to produce a Living Standard and Recommendation/Review Draft-snapshots
- WHATWG maintains the HTML and DOM Living Standards
- W3C facilitates community work directly in the WHATWG repositories (bridging communities, developing use cases, filing issues, writing tests, mediating issue resolution)
- W3C stops independent publishing of a designated list of specifications related to HTML and DOM and instead will work to take WHATWG Review Drafts to W3C Recommendations