Schema can be implemented thru RDFa and is considered the richer standard, but one that is a while lot more complex. With RDFA, some will argue that you get something more complete as it does not need to follow a standard body in order to be implemented, unlike microdata. Although some will say that the need for order in microdata makes for a much better designed code.
Another reason for sticking with RDFa is that you can use different vocabularies for the same item – something which can’t be done with microdata. With this feature in place, you can support both schema.org and the Open Graph Protocol of Facebook using one markup language.
One of the most successful uses of RDFa though is GoodRelations, a vocabulary used for e-commerce that standardizes the metadata of different vendors.
Schema can be implemented also thru microdata and is the most widely understood standard for structured data markup. Not only is it the variant most used, it’s also the most recommended one – by Google nonetheless.
The question then remains, when should you use it in your WordPress site? Given that it is the basis of schema.org, the answer should be immediately, right? However, the better answer would be to make microdata as your choice when you want something simple – something that is very easy to write, in other words.
But other than being fairly easy to write and understand, what else is there to microdata? For one, it’s best used if you’re just starting your site – even better if you’re still in the planning stages and such. You might ask, why is that the case?
You see, microdata is a manual process. You have to go into each of your pages to add this markup. Now, what if you have hundreds – or worse, thousands – of pages already? That would be quite the labor, wouldn’t it?
This is why site owners who are still in the process of creating their site and want to implement schema in the simplest way possible are better off with microdata. Also, if your site is already up and running but only consists of a few pages or so, then maybe implementing microdata wouldn’t be so much of a time-consuming effort for you.
You might also ask whether microdata should be added to every property of every page on your site. The simple answer is NO, but also keep in mind the very purpose of microdata: to help search engines understand your site a whole lot better. That said, implementing the standard in as many properties in your pages improves your chances in SERPs by a considerable margin.
Now that you’ve understood the differences…
When you put everything into perspective, both RDFa and microdata do the job of making your site more understandable to search engines, which in turn makes them display more relevant information in search results. All of these help your cause.
So, the final answer as to when you should use RDFa over microdata depends on what you want to accomplish with your site.