Marvel has more super scientists who claim insane IQs, but they tend to be savants. Reed Richards is great at science, but he's pretty dumb in a lot of ways.
On the whole, especially recently Marvel has placed a lot more emphasis in that area. Reed, Pym, Cho, that kind of IQ has gotten a lot of focus.
Its almost impossible to gauge since tech in DC seems to be more accesible for scientists, and its not that impossible to break boundaries of dimensions and time without cosmic artifacts. I would almost go as far as to say DC's dimensional barriers are much easier to pass through.
Firstly, I think you need to clarify what you're talking about here.
I think that DC's most popular characters are more powerful - Superman, Wonder Woman, Flash, Green Lantern, Martian Manhunter, etc.
I wouldn't say that DC is 'in general' more powerful than Marvel, I'd say that their powerful heroes are more VISIBLE than those at Marvel. You've still got SIlver Surfer, Thor, Beta Ray Bill, Gladiator, Quasar, Blue Marvel, Sentry (up until recently), etc roaming around the MU.
In that same way, I'd say that Marvel's more visible characters are smarter than DC's visible characters. You've got Reed Richards, Hank Pym, Bruce Banner (especially recently), Amadeus Cho, Valeria Richards, T'Challa, Dr. Doom, Tony Stark plus all the members of the Intellegensia, etc.
But by that same token, you've got guys at DC who can match pretty much any of those guys for feats (with the exception of Reed). You've got Batman, Lex Luthor, Ray Palmer, Will Magnus, Niles Caulder, Professor Ivo, Brainiacs 1, 2, 3, & 5, Sardath, Mr. Terrific, Steel, Anarky, Kilowog (who built a time machine and the Rocket Reds), Rip Hunter, etc.
I just doubt anytime anyone says 'omniscience'...it's such a vague term, and it normally doesn't mean much.
Is Eternity omniscient? If he is, why does he get trapped, beaten and generally treated like a child in almost every one of his appearances? Why does he have a worse win/loss record than Paste Pot Pete?
Strictly speaking only one being can be fully Omniscient. Two beings with Omniscience would share all the same knowledge and experiences and would be mentally indistinguishable.
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“Where the longleaf pines are whispering
to him who loved them so.
Where the faint murmurs now dwindling
echo o’er tide and shore."
-A Grave Epitaph in Santa Rosa County, Florida; I wish I could remember the man's name.