What was or still is the best API Portal & Reference that you have ever used?

Hello everyone,
I am currently serving as a product manager for a team that oversees an API Portal.
In my ongoing efforts to enhance our developer experience, I am reaching out to gather valuable insights from you regarding the most exceptional API Portals and References you've used.
When I refer to the "best," I have a few key criteria in mind that I would greatly appreciate your input on:

• Intuitive and Organized Documentation: I'm keen on understanding API Portals that boast a crystal-clear, easily navigable structure for their documentation and reference materials.
• User-Friendly API Portal Design: I'm particularly interested in instances where the design of the API Portal played a pivotal role in streamlining the extraction of vital information from its pages.
• Value-Added Features: If you've encountered API Portals that go above and beyond by offering features such as the ability to test API calls or providing functional API sandboxes, I'm eager to hear about them.

I encourage you to delve into the specifics of why you believe your chosen API Portal stands out as the best. Your insights will play a crucial role in shaping the future direction of our efforts.