Full disclosure: I now do some paid work for one of those CMS companies, so I don't want to give a biased answer :) I'm also not authorized to speak for them. What I can offer, though, is what I remember of our finalists of the Drupal migration project (what the parent post was about) -- that happened long before I joined the CMS company. Also keep in mind this info is from circa 2021-22; I haven't reevaluated since then and the players might've changed. That said:

* Contentful was by far the market leader. They were one of the first in the space, and probably the reason it got so big. Their UI was pretty decent, SDK and docs were good, support was good, good plugin ecosystem... but it was really expensive. When they started they were really affordable, but eventually I think they pivoted towards enterprise and wanted to wind down their more affordable plans. At the org I worked for, they wouldn't quote us an enterprise plan until we signed a NDA, and provided very limited developer sales/devrel time. My boss wasn't willing to continue with the sales process after that.

* DatoCMS was the most editor-friendly one, with a really nice UI, powerful field types, and a good admin interface with good roles & permissions & workflows that enabled complex user types to work in different parts of the CMS. Had a good plugin ecosystem, community support, and a small but really friendly and helpful team of staff. The sales process was great, with several of them sitting down with us to discuss all the details we needed. This was the editors' favorite in several ease-of-use categories. The primary concern there was that they're a relatively small Italian company instead of some huge American business (meaning potential time zone issues, etc.), but they'd been in business a few years already by that point and we were impressed by how supportive and welcoming they were.

* GraphCMS, now Hygraph, was what I considered the most technically powerful of the bunch. It had a really clean API, and was the only one (at least at the time) which allowed GraphQL mutations, meaning you could actually write to the GraphQL API. The others all needed REST APIs for updates, and provided GraphQL for reads. Its UI was pretty good, though a bit developer-centric compared to the others (like fields at the time didn't have editor-friendly labels, just their developer-facing names). The sales process was also great, and they were very accommodating of our questions.

* Prismic offered a really clean editor interface and stood out to me as the one that lets you jump right into editing the quickest. However, at the time, it didn't have some of the more advanced relationships / field types that we needed (don't recall the details, sorry). But I do remember it as "a CMS to revisit if I ever needed a simpler, cleaner one for a less complex schema" just cuz it felt so polished and easy.

* Wordpress with Advanced Custom Fields (a plugin), to my surprise, offered some of the most powerful AND easy to use schema, both in terms of the cleanliness of how it comes out in the API and in terms of how easy it was to compose/define in the editor and admin GUI. If data modeling were our chief concern, this would've been one of the top choice. ACF was really good, but we didn't want the baggage of Wordpress itself (i.e. having to host a LEMP & WP stack on Acquia or Pantheon just to run ACF headlessly; that'd be a waste of resources and dollars).

* There's a bunch of other commercial ones (Sanity, Storyblok, ButterCMS, Agility... see here for a list: https://jamstack.org/headless-cms/). In general they were all "good enough" and passed most of our criteria, but just didn't really stand out against our finalists. But that was just us, with our particular evaluation criteria and our specific individual editors' preferences. Before the eval, I built a prototype in many/most of these systems. I'd really encourage that! It really doesn't take long (it's so much faster and easier than in Drupal) and gives you a much better picture of what it's like to use each one, both as an editor and as a dev. Just define some good-enough schema (something like Northwind Traders, or even simpler https://en.wikiversity.org/wiki/Database_Examples/Northwind) and some basic frontend, then try to implement that schema in each service, fetch its data, and also try to programatically add/edit a record. I had a lot of fun doing that for about 20 different providers in the span of a week or so, and learned a lot along the way.

* There are also a few open-source/self-hostable ones if the cloud isn't your jam: the ones I remember were Strapi, Directus, and Ghost. There are probably more these days.