Since RFDa is not in the HTML5 spec yet, right now you can't make valid HTML5 websites that make use of RDFa.

But you don't have to use microdata or microformats; you can still use this schema with RDFa on an XHTML page.

You should be able to express everything in Microdata _and_ RDFa. I don't think RDFa is semantically richer than these other formats.