The controversial debate about Marvel vs DC often turns into a fight about popularity. I love both sides but let's be honest to ourselves.
So Marvel or DC?
The Marvel Universe would definitely win, no doubt . Not that DC ain't got great honorable heroes, just that, basically, the characters in Marvel Universe have inconmesurable power. Take a look:
1) Powerful cosmic entities, capable of destroying/creating worlds : Phoenix Force, Galactus (and his Heralds), the In-Betweener, Asgardian Gods, the Elders of the Universe, the Celestials, The Beyonder, Chaos and Order, Death and many, many more.
2) Omega level mutants, capable of changing the reality and alter minds:Legion, Franklin Richards, Hope Summers, Gabriel Summers, Nathaniel Grey, Jean Grey, probably Apocalypse and Cassandra Nova.
3) Cosmic artifacts, capable of... everything: the Ultimate Nullifier, the Infinite Gauntlet (with the Infinite Gems), the Cosmic Cube, the Nega Band and the Quantum Bands. Probably Mjolnir, the Tactigon and some other things around there.
And I didnt mention just powerful superheroes/supervillains like The Sentry, Hulk, Thanos, Ultron or Molecule Man. Neither I mentioned smart people like Reed Richards, Hank Pym, Bruce Banner, Tony Stark, Dr. Doom, The High Evolutionary, Armin Zola and many more. Or superheroes/supervillains that are not afraid of killing people like Wolverine, Psylocke, X-23, Bullseye, Fantomex, Sabretooth, Elektra or The Void (yes, that's The Sentry again, but we all know what he did with Ares).
So yes, Superman, very powerful. Batman, very smart. Flash, very quick. The New Gods, cool people. Darkseid, very scary. The Joker, crazy. Mr Myxzptlk, funny. The Anti Monitor... how many times has been defeated this guy?.
But Galactus could come to DC Earth and just eat it and be happy with that.