There's a few reasons why DC is superior to Marvel but the mains reasons....
Marvel....pretty much copies DC at every opportunity, be it characters or events.
There's entirely too many clones over at Marvel. Hyperion, Capt Marvel, MS. Marvel, Dr. Strange, Thanos, Nova and the Green Lanter...oops, the Nova Corps, Deadpool, Hawkeye,Xmen, Mavel Now in general, etc. Now, that's just the clones. I didn't count the "inspired by" characters. Take Hawkeye, for example. Hawkeye is a blonde haired Archer that is also a womanizer and dated Mockingbird, who is a blonde female martial artist. Green Arrow is a blonde haired Archer that is also a womanizer and dated Black Canary, who is a blonde female martial artist. One came long before the other. Now some like to argue that Doom Patrol predates Xmen by less than 6 months. Given Stan Lee's history, I don't think it's a stretch that he created the xmen based on what was happening at DC. The similarities between the two are...Uncanny! There's also Thanos, who pretty much IS Darkseid. They are the same character except Darkseid is obsessed with the Anti Life Equation and Thanos wants the Infinity Guantlet. Deadpool? A mercenary named Wade Wilson that wields guns and pistols and wears damn near the same costume as Deathstroke, who's a mercenary named Slade Wilson that wields guns and pistols.
In fairness, DC has copied Marvel. Blackest Night is basically Marvel Zombies and Namor was around long before Aquaman. But Marvel takes it's copying to a whole new level.
My other reason is that Marvel milks the hell out of there franchises. There's Avengers, New Avengers, Young Avengers, Secret Avengers, Dark Avengers, A+X, Avengers Assemble, Uncanny Avengers, and Avengers Arena. The Xmen are even worse. There's X-Men, All New X-men, Uncanny X-men, Astonishing Xmen, Wolverine and the Xmen, Xmen Legacy, X-treme Xmen, Ultimate Comics Xmen, Cable and the Xforce, Uncanny Xforce....WAIT... You read that right. TWO DIFFERENT XFORCE BOOKS
And of course there's...Amazing Spiderman, Superior Spiderman, Avenging Spiderman, Scarlet Spider, Ultimate Comics Spiderman, Ultimate Spiderman.
In fairness, there's 4 current Justice Leagues, 5 Batman comics, 2 Superman, and 3 Green Lantern books. That's bad, but not nearly as bad as what Marvel does.
Lastly, the storylines in Marvel...are completely underwhelming. Take Age of Ultron, for example. If you've at least heard about the comic, you know where it's headed. I've only read a few issues and I already can guess there will be time travel involved or some alternate universe crap. A vs X started out EPIC, but the end result is a few mutants losing there powers, the Avengers realizing they are all assholes, Xavier retires..again, and Wokanda takes a pounding. Only one person died and there was some shit about dragons...