Marjane Satrapi’s Persepolis secured the top spot on a list of "The 50 Greatest Graphic Novels of All Time" compiled by The Herald of Scotland, which surveyed an undisclosed number of “cartoonists, novelists, critics, journalists, comic historians, comedians, and the odd musician” in order to come up with the rankings.  There are more than a few surprises on the list (From Hell is ranked ahead of Watchmen), and there is a definite European bias (manga is represented only by one volume from Otomo, one from Tezuka, and Barefoot Gen), but it is instructive nonetheless.
Here from Scotland's Sunday Herald's list are the first 15 of the "Top 50 Graphic Novels of All Time:"
  1. Persepolis (Marjane Satrapi)
  2. Maus (Art Spiegleman)
  3. Jimmy Corrigan, The Smartest Kid on Earth (Chris Ware)
  4. Black Hole (Charles Burns)
  5. Ghost World (Daniel Clowes)
  6. From Hell (Alan Moore & Eddie Campbell)
  7. Locas (Jaime Hernandez)
  8. Watchmen (Alan Moore & Dave Gibbons)
  9. V for Vendetta (Alan Moore & David Lloyd)
  10. Palestine (Joe Sacco)
  11. Akira (Katsuhiro Otomo)
  12. Batman, The Dark Knight Returns (Frank Miller)
  13. The Nao of Brown (Glyn Dillon)
  14. Epileptic (David B)
  15. The Incal (Alejandro Jodorowsky & Moebius)
Other American titles to make the list include Chris Ware’s Building Stories (#17), David Mazzucchelli’s Asterios Polyp (#18), Alison Bechdel's Fun’Home (#22), Will Eisner’s A Contract With God (#25), Julie Doucet’s New York Diary (#31), Brian K. Vaughan & Pia Guerra’s Y: The Last Man (#32), Bill Watterson’s The Complete Calvin & Hobbes (#33), Garth Ennis and Steve Dillon’s The Preacher (#34), Craig Thompson’s Blankets (#36), George Herriman’s Krazy Kat (#39), Frank Miller’s Sin City (#49), and Paul Pope’s Heavy Liquid (#50).