One of the events you may have missed from Comic-Con International in 2010 was that the Guinness Book of World Records added Marvel Comics to its latest edition for publishing the best-selling comic book of all time: X-Men Vol. 2, #1, with its five variant covers in 1991. A ceremony was held at the event, with writer Chris Claremont in attendance. (Marvel has a video interview with the Guinness editor here.)
The ranking of X-Men Vol. 2, #1 has been mentioned by me many times, here on the site and in my previous work for Comics Buyer's Guide. The 8.1 million copy figure could even have come to their attention from one of my past reports, for all I know; I drew it from Marvel's internal 1991 records, myself. Here are the breakdowns for how the issue sold:
Within the direct market sales, Capital City Distribution's sales of each edition ranged from 424,800 copies, for the Beast cover, to 332,800 copies for the Magneto cover: its overall sales were 1,874,100 copies, or 23.3% of all direct market sales. (There were a dozen different distributors selling to comics shops then). Note that there were no newsstand sales of the fifth cover. The newsstand draws of the issue in general are far lower than the normal newsstand/direct market breakdowns seen in 1991; it's apparent that the newsstand didn't read the same demand for the new title that comics retailers did. The overall newsstand draws are about 60% above what Uncanny X-Men's were at the time; I'm guessing that title was used as an ordering guide.
All five versions of the issue (whose four covers combined to make the single image represented in the fifth, double gatefold cover edition) released in consecutive weeks of August 1991. There were also no subscription sales reported, as it was a brand new title. There is no American rival to X-Men #1 for this title; there are comic books in the 3-4 million copy range (like X-Force #1, only two months old when the "adjectiveless" X-Men title launched), but I know of nothing with numbers like these. (The reprinted issue has been collected here.)
Guinness would seem to be defining a comic book as a periodical magazine, as opposed to any other delivery system which contains comics content. That's certainly in line with how the term has always been used in this country: Watchmen #1 is a comic book. Watchmen is a collected edition — and it is also a graphic novel. One is on sale for a month. The other is on sale forever. This is a key distinction, when it comes to making sure we're making apples-to-apples comparisons — and it is important when considering comparisons with international top-sellers such as One Piece and Asterix editions.
Frequent mention is made in the trade press of the sales records of the Japanese manga series One Piece, which are spectacular indeed: Anime News Network reports that Eiichiro Oda's latest edition, One Piece Vol. 60, sold more than 2 million copies in its first week of sales this month out of a record first printing of 3.4 million copies. All the volumes of the series have sales of more than 200 million copies combined.
seems to have peaked in the mid-1990s, with the peak sales for a single issue being 6.53 million copies in 1995.
I would tend to regard the "phone books" as a distinct delivery system from the traditional American comic-book-held-together-by-staples; they are, in many senses, books on their own. There have been American anthology monthlies — indeed, comics began as anthologies — but most topped out at 80 pages, and few have been seen in recent decades. But it is proper to say that Shonen Jump provides a somewhat closer comparison to X-Men Vol. 2, #1 than One Piece does — and there, X-Men #1 holds the edge.
On the other hand, any given One Piece tankouban is more appropriately compared to sales of Watchmen and similar collected editions. According to Brian Hibbs, Watchmen sold 424,814 copies of its softcover collection in 2009 through just those stores that report to Nielsen's Bookscan; while its all-time sales are higher still, it's probably safe to assume that with One Piece's first printings so monumental, there are individual tankouban in those 60 volumes that have outsold it over time.
I think the takeaway is that One Piece, as a tankouban, stands a good chance to be the international record-holder when it comes to bound-edition bookshelf comics (without undertaking an exhaustive survey of all European and Japanese comics, I can't go farther than that), while X-Men Vol. 2, #1 very likely holds the worldwide title when it comes to periodical newsrack comics with staples.
An interesting question is how comparisons can be made series-wide. If individual tankouban can't be compared to individual comic books, how does One Piece as a 200-million-copy selling series stack up against other series historically? Or its sales of 14.7 million copies, series-wide, in 2009?
extremely long-running British weeklies whose sales over time would be considerable; there are other European titles you'd want to look at, too. But just comparing with series with a single star, we know that Superman sold in the 15-20 million range annually in the 1950s, and had sales in just the 1960-1986 years of more than 110 million copies. All told, from 1939 to present, the title is almost certainly north of 200 million copies, if not 300 million — not counting all reprints of that material. And that's where it gets pretty easy to get off into the weeds, trying to decide what should be counted. Foreign editions? Many Disney comics which began in the high-circulation 1940s and 1950s would be in the running. Heck, if we enlarge the comics definition, Mad was definitely having 25-30 million copy years for a while there in the heyday.
An interesting, endlessly debatable topic for discussion — and the nice part is that is it reminds us of the potential reach of comics as a medium. To a degree, anyway: a huge portion of those X-Men comics were purchased not by readers, but speculators: one I'm aware of bought 5,000 copies, not realizing it would be the least scarce comic book of all time. I have 25 copies in my own collection, and I only bought one — I have no idea where the others came from!