We are using strapi currently, it's relatively popular and it's js, serves us well so far for the few projects we've used it on.
Been using Sanity CMS as a freelance web developer for a little over a year now. I love it and my clients love it. There is a small learning curve at the start but once you're past that its an absolute pleasure to work with.
https://www.reddit.com/r/reactjs/comments/170giuv/whats_your_goto_headless_cms_and_why/