Love your work. The reason why I am going with the static ones is because of the fact that motion ones can load slower and that affects SEO on some of these articles.
The motion ones are great for twitter and other social media platforms though.
Just something to consider as you are developing stuff. Different use cases for each.
Now you can imagine how hard is upload some gifs, it's not easy pick a video motion and convert to gif without losing quality and get the right size to upload, any gif above 7 or 8Mb it's almost impossible to upload.
And you're right! never had thought in terms of SEO.