Men at War is a series of World War II novels created by W. E. B. Griffin in 1984.
 More recently, the series newest novels were co-authored by his son, William E. Butterworth (under the name William E. Butterworth IV).
 Originally, the series was written under the pseudonym of Alex Baldwin.
 Some editions of the books listing Baldwin as the author contain cover blurb quotations, attributed to Griffin, praising the books (i.e., he is praising his pseudonymous work under another of his pseudonyms.)
Xanth ( ) is a fantasy world created by author Piers Anthony for his "Xanth" series of novels, also known as "The Magic of Xanth".
 Anthony originally intended for Xanth to be a trilogy, and after the success of the first three books expanded the series to nine books.
 A devoted fan base persuaded the author to continue writing the series, which is now open-ended.
Xanth is a fictional universe created by author Piers Anthony.
 It is a magical land most often described as being shaped like the state of Florida.
 The geography of Xanth is, therefore, very similar to that of Florida.
 As is typical with the series, many geographical landmarks are puns based on real-world locations.
 As an example, the "With-A-Cookie River" in Xanth is roughly parallel with the Withlacoochee River in Florida.
William Edmund Butterworth III (born November 10, 1929), better known by his pen name W. E. B. Griffin, is a writer of military and detective fiction with 38 novels in six series published under that name.
 He has also published under 11 other pseudonyms and three versions of his real name (W. E. Butterworth, William E. Butterworth, and most recently William E. Butterworth III).
Apprentice Adept is a heptalogy of fantasy and science fiction novels written by English American author Piers Anthony.
 The series takes place on "Phaze" and "Proton", two worlds occupying the same space in two different dimensional planes.
 Phaze is a lush planet of magic, where Proton is a barren mining planet of science.
 As the series opens, each person born on Phaze and Proton has an alternate self living on the other world.
 But if a person on either world lacks a duplicate (for instance if a Proton citizen immigrated there from another planet, or a counterpart from the opposite frame died), he can cross to the other through an energy "curtain" that circumscribes each frame.
Air Apparent is the thirty-first book of the Xanth series by Piers Anthony, which was first mentioned in the "Author's Note" in "Currant Events".
 Piers Anthony stated that notions from his readers have already been set aside for use in this installment in the same "Author's Note."
Chthon is a science fiction novel by American writer Piers Anthony, originally released in 1967.
 It was Anthony's first published novel, and was nominated for both the Nebula Award for Best Novel in 1967 and the Hugo Award for Best Novel in 1968.
This is a partial list of works by Piers Anthony.
 Anthony has published 166 works in total from 1956 to December 2013.
Cameron Pierce (born May 23, 1988, Bakersfield, California, United States) is an American author of bizarro fiction currently residing in Portland, Oregon.
 The "Bizarro Starter Kit (Purple)" described his work as "Surreal nightmares that are funny, sad, sincere, and violent."
 His work has been praised by Troma founder Lloyd Kaufman, Piers Anthony, "The Guardian", Cracked.com, "Details" Magazine, "New Times", and SF Site.
 In 2011, his short story collection "Lost in Cat Brain Land" won the Wonderland Book Award for Best Collection of 2010.
 Pierce is also the editor of Lazy Fascist Press.
Piers Anthony Dillingham Jacob (born 6 August 1934 in Oxford, England) is an English American author in the science fiction and fantasy genres, publishing under the name Piers Anthony.
 He is most famous for his set in the fictional realm of Xanth.

Question: Which author has used more pseudonyms, W. E. B. Griffin or Piers Anthony? 
Answer: W. E. B. Griffin