Microdata or JSON-LD? I'm confused

Consumers that support Microdata support Microdata, no matter if or where Microdata is specified.

It’s conceivable that new consumers might decide not to support it, but the syntax is still very popular and still part of WHATWG’s HTML Living Standard, so it’s probably not going to vanish.

About the consumer Google

Some years ago, JSON-LD was not supported for many of their features, and they recommended that authors use Microdata (and they supported RDFa, too). Today it’s different.

See Google’s Markup formats and placement:

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.

According to the mentioned table, Microdata and RDFa support all of Google’s data types, while JSON-LD supports everything except their Breadcrumbs feature.

I wouldn’t give much weight to their recommendation. They say that "Structured data markup is most easily represented in JSON-LD format", but I think it’s safe to say that this only applies to authors that generate the structured data programmatically (especially from tools that support JSON).
For authors that manually add the structured data markup, it’s typically easier to use Microdata or RDFa, and using these syntaxes minimizes the risk that an author updates the content without updating the structured data, too (see DRY principle).

JSON-LD vs. Microdata vs. RDFa

Unless you know (and care for) consumers that don’t support all three syntaxes, it doesn’t matter. Use what is easier for you and your tools.

If you have no preference, I would say JSON-LD or RDFa, because contrary to Microdata,

• both are W3C Recommendations,
• both can be used in non-HTML5 contexts,
• both allow to (easily) mix several vocabularies.

JSON-LD if you like your structured data not "intermingled" with your markup (= duplicating the content), RDFa if you like to use your existing markup (= not duplicating the content).

I've opted to go for JSON-LD because it is easier to read and compile. Spotting errors is easy for more complicated dictionaries. It is the W3C and Google recommended standard.

One caveat (major if you need to support it), is that as of May 16 2017, Bing STILL doesn't support JSON-LD