A survey of top 10 million websites reveals that only 25.1% of websites use JSON-LD structured data. Google has expressed that JSON-LD is their preferred structured data.

JSON structured data can be inserted in the head as well as the body of your pages, Webmaster Trends Analyst John Mueller explained on the September 11 edition of #AskGoogleWebmasters. The question.

Google’s stated preference is for JSON-LD. It may be in your best interest to consider switching over to JSON-LD structured data if you currently use microdata.