It's complicated

These days I prefer DC personally, but, listing the positives and negatives here helps to show that.

DC - Started the superhero genre. Their trinity characters survived the hard times after the CCA. The first superhero team, the JSA. DC ushered in the revised Golden Age heroes in the Silver Age. More than any other publisher, DC has acquired its competitors and incorporated them into the DCU, including All-American, Quality, Fawcett, Charlton, and Wildstorm. DC has had many different imprints attempted to appeal to different market segments including Vertigo, Helix, Wildstorm, Minx, Focus, Piranha Press, Mad, the Will Eisner Library, Young Animal, First Wave, !mpact, Milestone, Zuda, and Paradox, among others. First publisher to have introduced the multiverse concept with Earth-1 and Earth-2 and a shared continuity.

Marvel - May not have started the genre, but under Stan Lee, given it new life, bringing more depth and characterization and more actively linked stories across the publishing line. Stan was the Editor-in-Chief and oversaw the entire Marvel Bullpen in the Marvel Age. Working with Jack Kirby and Steve Ditko, created the most popular pantheon of superhero and supervillains characters collectively, which for the vast majority of the last 40+ years, has been the best selling line of comics. Though it has had genre diversification, Marvel has focused mostly, and mostly succesfully, doing what it does best : superheroes. Came out of bankruptcy and continued to successfully rebuild and eventually established its own movie studio, Marvel Studios, which has helped it to increase its share of the market both in publishing as well as in cinema. Acquired Malibu Comics and the rights to characters Angela and the Marvelman family of characters. Created Epic Illustrated to compete with Heavy Metal magazine, and later branched off Epic Comics allowing creators to retain the rights to their creations, and later added the Icon imprint.