Which one, given what you have
A marketing team that builds its own landing pages. Storyblok. This is what it is for, and the block library means giving people that freedom does not cost you the design system.
Six markets, three brands, a large editorial department. Contentful. The locale model and the permissions are the product, and the $300 step is small next to what the alternative costs in duplicated work.
A growing team on a budget. Storyblok gets you moving for less, but check the ceiling first. Because the seat maximums are walls rather than prices, the cheaper entry point can become a forced migration at exactly the wrong moment.
Content that is data rather than pages. Contentful, or neither. A product catalogue or a research library gains nothing from visual page assembly, and you would be paying for Storyblok's defining feature while never opening it.
A codebase where an AI agent does much of the work. Storyblok reaches further, since its MCP server covers component schemas, roles and space configuration rather than entries and types alone. Neither keeps the model in your repository, so both leave an agent querying an API to discover what the model currently is.
What neither of them gives you
On both platforms the content model lives in the vendor's database and your files are a copy of it. That means no pull request review of a schema change, and no guarantee that what is committed is what is running. If that property matters more than either platform's headline strength, this comparison is the wrong one and Payload, Strapi or Sanity is where to look.