What to use as a identifier for researchers?
What are the most professional, persistent, and commonly used researcher profiles in academia?


Name, surname and current institution. :) 

Everything else is just a new fad that may not stand the test of time. Although, among those that you cite, Orcid has the most potential because:


it is explicitly designed to be persistent and used for disambiguation;
its functioning and access model is more open than those of the competitors, and because of this many independent services have started integrating it;
it is backed by a large consortium of publishers and organizations, including those who make Scopus and Web of Science and most of the other (currently) big players in the publishing business.


If you are worried about proving that you wrote the document and not someone else with the same name, consider including a short bio and a profile picture, like it is sometimes done in journals.