Various is the correct author for any book with multiple unknown authors, and is acceptable for books with multiple known authors, especially if not all are known or the list is very long (over 50).
If an editor is known, however, Various is not necessary. List the name of the editor as the primary author (with role "editor"). Contributing authors' names follow it.
Note: WorldCat is an excellent resource for finding author information and contents of anthologies.
Some marvellous perceptive writing in this collection of forewords to Folio Editions. John Sutherland on Slaughterhouse Five, Iain Sinclair on The War of the Worlds and, best of all, Julian Barnes on Ford Madox Ford’s The Good Soldier: “We must prowl soft-footed through the text, alive for every board’s moan and plaint...This is a novel which proceeds, both at phrase-level and in terms of plot and character, by moments of disorienting readjustment, some sly and secretive, others dazzlingly brazen. Facts yield and deliquesce before impressions; impressions are quashed by subsequent facts. What can we know.”