I have been using Jekyll since 2015. Jekyll is not dead, but it might be feature complete. The fact that Github is supporting Jekyll is very important. It makes Jekyll a very good choice. Jekyll is also quite fast.
Personally I have made the switch from Jekyll to Hugo, but Hugo is less evolved. Hugo is quite hard to understand, even for the people who are very much into it. Also, I have found that you are not able to use a directory structure when using the multilingual feature (alternative permalinks in the config). To me this is clearly a bug. The reaction to this on the forum was rather negative (which is another reason to choose for Jekyll):
I have never found inconsistent behaviour in Jekyll and I have built hundreds of websites with it. People have always been very helpful. There are SO many sources on Jekyll (including SO) and it is used on a lot of websites. Although I like Hugo for its speed, there is no clear reason NOT to use Jekyll.