Of lithography, serigraphy and seriolithography, is one more valuable than another?

Answer 1

Great answer Bob, value also might depend on the size of the edition? (Smaller editions having a higher "perceived value" than large editions)

Answer 2

Are you asking in terms of collecting value? Or resale value? All of the processes in your question fall into the category of "prints" and are generally less valuable in terms of resale than paintings.
For a proper understanding of the seriolithographic process, go to
http://www.mfatalon.com/seriolithography-services.html.
Lithography (the process known as "stone lithography") is the oldest of all three processes and generally more valuable than the other two. Serio-lithography is the newest of the processes mentioned and is a combination of silk screening and stone lithography. Serigraphy (silk screening) is generally not as valuable as a print than the traditional print processes like etchings, stone litho, or engravings.