I've used WordPress for years. It's great for a simple blog, but not any kind of complex CMS, IMHO. After adding a few plugins, maintaining it is a nightmare; and I won't get into the database design underneath.

Another vote for Wagtail: my team has moved to it and have found it to be wonderful. It is the first time our tech, content, UX and marketing teams all agree on a CMS being wonderful. Streamfield is an absolutely killer feature. Our writers love the editor interface, which was clearly designed by and for content creators, and not by a bored developer like me.

Check out Wagtail. It takes a little bit more planning to get started, but wow, does it pay off in the long run.

It is truly free and open-source, released under the BSD license.