Marvel Legacy #1 was September 2017's top-selling print comic book according to Diamond Comic Distributors and new estimates from ComicChron peg it as the top-selling book of the entire year so far. ComicChron
estimated that the $5.99 one-shot amassed 298,242 copies by Direct Market retailers, beating out the previous highest-ordered comic book - September's Dark Nights: Metal #1 at 261,997.
Those numbers include Marvel Legacy #1's various covers. Since they were all the same price, Diamond Counted them as one edition on their sales charts. In contrast, September's Action Comics #987 and #988 had different price points for their variants, leading the distributor to seperate their numbers as separate editions. If grouped together the issues would have ranked a higher 7th and 8th for the month, respectively.
As with all of Diamond's sales figures, those numbers only account for initial orders from North American comic book retailers and doesn't include re-orders or reprintings, or sales to consumers. Marvel Comics has not notifed retailers of any second edition reprints of Marvel Legacy #1.
Going deeper into the charts, ComicChron notes that lower level titles - specifically ussing the 100th place sales slot as a barometer - are up. September 2017's 100th place was Nightwing: The New Order #2 at 25,027 estimated copies - the first time a 100th place book has sold over 25k copies since 1999.