Sanity and Strapi are amazing. Especially with Sanity having their sanity.io/create
Sanity probably has the faster setup time. Strapi isn't far behind though.
Strapi does a great job being an app backend. Custom content types + relationships + ability to do custom things on models by diving into the code.
Sanity is amazing for sites like blogs, portfolios, ecommerce.
They are both great tools; all depends on what you're trying to build