What's Most Important When Picking an API?

Hey all, when you are picking an API, provided it's your choice and money is no option and assuming they all scale well, have great uptime promises, low latency, and no known security issues, which of the following following factors matter most to you? Feel free to add your own.

• Fast / easy signup
• Time to first hello world
• Quickstarts are easy and intuitive
• Tutorials
• Accompanying tools (like a debugger, a dashboard)
• Sandbox environment to playtest before you "buy"
• API follows standards / best practices that you recognize
• Documentation (thorough and clear)

If you want to add extra thoughts as to why, you get bonus points. :D

Thanks!