JSON-LD is the recommended format. Google is in the process of adding JSON-LD support for all markup-powered features. The table below lists the exceptions to this. We recommend using JSON-LD where possible.
But in other article, in the What is microdata and JSON-LD markup? section, they say they prefer microdata for content:
Microdata and JSON-LD are two different ways to mark up your data using the schema.org vocabulary. It's best to choose either microdata or JSON-LD and avoid using both types on a single page or email. Google prefers microdata for web content.
So what's up?