What's the best headless CMS to integrate into React/Node stack for web dev?

I recommend checking out Strapi [1], very powerful, open source, clean API generator.

I've researched this a ton recently. My current frontrunners (they change often) are:

Directus for complex schemas (something more like a CRUD app)

DatoCMS for something more like publishing

Although honestly React is not the right framework if you're just building an informational site, especially when SEO is important.

Try Pantheon hosting drupal 9, very easy and visual to create REST endpoints and their free tier will be a cherry on top.