Over the years, Google has gone from recommending uploading a text file, to parsing RDFa with a slightly modified Microformats vocabulary, to going all-in on Microdata, to then replacing Microdata with JSON-LD and the new Schema.org vocabulary. In the mean time, the Microformats hReview vocabulary hasn't changed, and has continued to be parsed by Google since it is so widely deployed. It would seem there is some advantage to using a format that was developed externally from Google, since they are unable to simply turn their backs on it and replace it with a new format whenever they want. For this reason, I'm sticking with publishing the Microformats 1 hReview markup for my reviews.

RDF Translator is a multi-format conversion tool for structured markup. It provides translations between data formats ranging from RDF/XML to RDFa or Microdata. The service allows for conversions triggered either by URI or by direct text input. Furthermore it comes with a straightforward REST API for developers.

This [html-extensions] specification defines new HTML attributes to embed simple machine-readable data in HTML documents.