Sanity was actually the first CMS we considered. In diving deeper, it's more of a document database (and what we're building is incredibly relational database-heavy) so we'd be building the structure of our database more based on Sanity than what we actually need.
Many of these headless CMS solutions are actually quite opinionated in the database architecture you use, even if they are BYODB (Bring Your Own Database), which was a bit disappointing the further we dug into it.
That's where Payload CMS and Directus CMS came out as the two most ideal options for us, as they aren't opinionated in the database architecture and allow you to build your own DB structure.
Same downside with Contentful CMS and even Strapi CMS in digging down further.
All-in-all, while Sanity has one of the most pretty marketing sites/brands, the actual backend UX when playing with it felt quite a bit older and outdated than some of the others.
Power anything from websites to internal tools with the open-source backend & modern admin UI that you truly own.
If you're looking for a modern CMS solution and the words "open source", "built in NextJS", and "Vercel" are all music to your ears, Payload CMS is the best option available on the market.
They are re-imagining what a CMS should be using the most modern tech, and shaking up the space that has otherwise been quite stagnant.
What Makes Payload CMS different from many other CMS solutions on the market is that it's fully open source and works fully serverless, so you can host it right alongside your app on Vercel, or whatever your serverless hosting provider of choice is.
They were built out of necessity as an internal CMS for a web development agency as they weren't happy with existing solutions on the market, and then decided to go through YC to raise funds and turn it into a full standalone company, now being used by behemoths like Disney and Bugatti. Not to mention, it's what we're using for our site rebuild here at Efficient App.