Which one, given what you have
A product team with developers, publishing to a custom front end. Sanity, without much hesitation. The schema in version control and an editor shaped to your content are worth the build phase, and at that team size the per-seat bill is small.
A marketing department with no engineering support. Contentful. Sanity has no editing experience until somebody creates one, and a team that cannot create one is buying a blank page.
One brand, one language, one site. Neither is an obvious answer, and both are more platform than the job needs. Look at Storyblok if the daily work is assembling pages, or Strapi if you would rather own the whole thing.
Several markets, several brands, a large editorial team. Contentful, and the $300 step stops being the deciding factor. What you are buying is the locale model and the permissions, and nothing on the other side of this page replaces them.
A codebase where an AI agent does much of the work. Sanity, because a schema an agent can read in the repository beats one it has to query an API to discover. Both expose the content model over MCP, which is more than most of this category, but only one of them also leaves the model in your git history.
The question that settles it
Ask who will change the content model in eighteen months, and where you would look to find out what changed. If the answer is a developer and a pull request, that is Sanity. If it is a content lead and an audit log, that is Contentful.