A few years ago Marvel introduced super-genius Amadeus Cho who was supposedly “the seventh smartest person on Earth” (later changed to the eighth).
It was never supposed to be considered a serious ranking, as explicitly told in later stories, but that got me thinking. How WOULD you rank the super-geniuses of Marvel and DC?
Some ground rules are necessary:
A) Versatility matters. Being at the top of one field but being just okay in others is not the same of being at the top in multiple fields.
B) Actual feats trump potential. If a character is clearly absurdly smart but hasn’t done many impressive things, that hurts the ranking.
C) No artificial intelligences, time travelers and gods. They kind of cheat and are very difficult to evaluate.
D) I’m exclusively considering science. Geniuses in other fields get honorable mentions, though.
E) I’m evaluating Marvel and DC separately since the two universes run with separate rules.
This is just for fun, and the ranking can very easily change a lot.
I will defend the top two for both companies, though.
DC COMICS
Let’s start with DC since I have far less characters to evaluate: a combination of super-scientists being REALLY popular at Marvel, and my general knowledge of the universe.
This is a VERY simplified list: even with the above rules, I’m probably leaving out some important names.
NOT ON THE LIST: Batman
Stop putting him on this kind of lists: he’s not THAT smart! Sure he’s way smarter than average, he’s the World’s Greatest Detective, and could probably defeat the vast majority of people in this list on his own… but I wouldn’t consider him a “super-genius”.
I mean does Batman think he’s THAT smart?
HONORABLE MENTIONS: Karate Kid and Cassandra Cain
The two super-geniuses of martial arts. Karate Kid is by default the best martial artist of an entire galaxy, and this version of Batgirl could probably give him a hard time in a fight.
There are other super-martial artists in DC Comics (chief among them Lady Shiva), but these two reached the top when they were teenagers. 
#10: Barbara Gordon
She’s QUITE distant from the others on the list. But her tenure as Oracle proved she was absurdly smart at anything regarding computers. 
#9: The Brain
We’ll see him soon in the Doom Patrol retrospective. Despite lacking a physical body (most of the time) he comes off with truly bonkers inventions. His nemesis Niles “Chief” Caulder is either at his level or slightly smarter, but this is a simplified list. 
#8: Gorilla Grodd
Considering I’m excluding time travelers, the smartest Flash villain. Easily the smartest gorilla from Gorilla City, which itself is inhabited by geniuses. 
#7: Mr. Terrific (post-Crisis)
I’m not super familiar with him, but as far as post-Crisis geniuses go he’s impressive. He doesn’t reach the reality-breaking levels of the upper ranks, but when you’re the second choice of the entire superhero community when it comes to solving science problems, that counts! 
#6: Ray Palmer
The FIRST choice of the entire superhero community when it comes to solving science problems. Not too many crazy inventions of his own, but this guy is probably as smart as you can get without running into sheer absurdity.
#5: Superman (Silver Age)
The post-Crisis one is far from being dumb, but Silver Age Superman had super-intelligence as an outright superpower. Plus he was CONSTANTLY shown to be running all sorts of experiments in the Fortress of Solitude. This version of Superman could make world-changing inventions on the fly, in his spare time, just for fun. 
#4: Brainiac (Silver Age only)
Later stories turn him into a robot, which disqualifies him. The post-Crisis version doesn’t reach the same levels of ridiculousness until he goes full cyborg, which complicates things.
The pre-Crisis version, however, could come up with inventions for which Superman could not figure out a counter, even after decades of work: his force-field and his shrinking ray specifically. 
#3: Brainiac 5
I would argue that the Silver Age version is not as smart as his ancestor. But if we get to later years, and especially later incarnations? Probably as smart as a hero can be without having you question how he doesn’t fix everything. And of course there’s being considered a super-genius by an entire planet populated by insufferably smug super-geniuses. 
#2: Lex Luthor (Silver Age)
At least Brainiac 5 follows logic and employs stuff that can be considered science. Lex Luthor builds time machines with random junk he finds around!!!
#1: Doctor Sivana (Golden Age)
As I touched on my review of his first story. Sivana is basically a reality warper of the highest order. 
MARVEL
Despite the length, this is NOWHERE NEAR a complete list.
NOT ON THE LIST: Professor X and Magneto
I often see them among super-geniuses. They’re both definitely smarter than average (Xavier especially, although I’m pretty sure in the latest continuity he wasn’t the one to build Cerebro) but to me they don’t belong in this list.
HONORABLE MENTIONS: Doctor Strange and Squirrel Girl
The first one needs no explanation. When GALACTUS calls you as the magic expert, you know better than literally anyone in the universe.
But I’m also giving props to Squirrel Girl thanks to her “Unbeatable Squirrel Girl” series, where she CONSISTENTLY defeats enemies that should be waaaay above her level by just sheer logic. 
#???: Moon Girl
Supposedly the smartest person on the planet, able to solve super-riddles that even Reed Richards could not solve. But I can’t easily fit her in the rank because I haven’t read many of her stories; plus she’s still a kid and therefore hasn’t had the time to do much, AND her stories are more light-hearted than most superhero series. If all the talk about her potential turns out to be true, she could be in the top three. But it’s too early to tell.
(also I haven’t watched her cartoon yet, but reportedly it’s very good) 
#20: Sage
One of Claremont’s most bizarre retcons is revealing that a VERY minor member of the Hellfire Club was actually a mutant with a computer-like brain. Which I guess kind of makes her Marvel’s Brainiac 5, but she doesn’t get any absurd feats. Still, her powers makes her a “jack of all trades” kind of character in anything even remotely connected to actual science (not so much bulls#it super-science). 
#19: Ironheart
Riri Williams was introduced as the genius 16 year old who reverse-engineered Iron Man’s suit which is QUITE an accomplishment. I haven’t read a ton of her appearances besides her very brief stint as Iron Man’s de facto substitute, so I don’t know if she’s done something particularly insane later.
#18: Forge
His vaguely defined mutant powers of “being really good at building stuff” almost qualifies as cheating, but he’s come up with interesting stuff AND knows a little bit of magic.
Plus he’s the only one on the list who threatens Tony Stark for the best moustache.
#17: Peter Parker
Spider-Man is all over the place depending on the writer. Sometimes he’s just really smart, sometimes he’s a world-class genius in chemistry, sometimes he’s a super-genius at everything. I don’t like stories that put him TOO high in this regard, but he’s consistently able to work with your typical super-geniuses without coming up with too many crazy ideas on his own.
I haven’t read much of his stories after One More Day; I’m pretty sure some of those would put him higher on the list. 
#16: Beast
It took a long time before Beast was invited to work with other super-geniuses but he definitely qualifies. Just like Spider-Man he was coming up with absurd inventions as a teenager (like a device to amplify mutant powers). I see them as basically equal, but while Spider-Man sometimes goes to Beast for scientific help… the reverse doesn’t happen, so Beast might just be either a little bit smarter or a little bit more experienced. I would say the latter, since he gets to be in a lab far more frequently than Spidey.
#15: Arnim Zola
When it comes to genetic tampering, there are many candidates for the best. I could’ve gone with the High Evolutionary or Mr. Sinister, but the former cheats by turning himself into a god and the second… could he build robots with 1940s technology? I don’t think so, meaning Zola wins thanks to versatility. And as good at biology Spider-Man and Beast are, they don’t get anywhere near the stuff Zola creates. Mostly because he makes monsters and clones nazis, so who would WANT to copy him?
#14: Mad Thinker
He might not be as good at genetics at Arnim Zola and he admitted to stealing inventions from smarter people… well, just from Reed Richards really… but his androids are unmatched in the Marvel Universe by anything not built by Ultron or Doctor Doom. His ability to bulls#it his way out of convoluted explanations predict the future by just thinking really hard, plus the fact that unlike most supervillains he can carry out his plans while still in prison, adds to the versatility.
#13: Red Ghost
Could Arnim Zola or the Mad Thinker build their own spaceship AND train three apes to become his supervillain henchmen? I don’t think so.
#12: Doctor Octopus
Poor Otto Octavius. In a different universe, he’d have no problem being THE smartest man in the world… but the Marvel Universe is too insane for him.
Still, he’s come up with impressive stuff over the years, especially in the 2000s. He’s enough of an expert on radiation that Reed Freaking Richards wanted his help when Susan was having health issues during her pregnancy, and he’s come up with all kinds of serums and robots.
I don’t doubt that he could build his own spaceship or train apes. Not too impressive when it comes to artificial intelligence stuff, but he was big in virtual reality in the 90s. It was the 90s.
#11: Amadeus Cho
The kid who started this whole idea, originally declared the seventh smartest person on Earth and then losing the position to Hank Pym.
Another computer mind like Sage, but unlike her he has a better record and lots of crazy inventions. His super-intelligence doesn’t get enough play now that he also has Hulk powers, but he’s still way smart. 
#10: Bruce Banner
In the Silver Age he’s not too crazy: he builds a robot or two, but for the most part he’s just a physicist. It’s the 2000s that REALLY hype him, especially whenever he loses the ability to turn into the Hulk. When none other than DOCTOR DOOM considers you an expert worth asking for help (not with these exact words of course), that’s huge!!!
He also ALMOST confirms my list, calling Amadeus the tenth smartest. 
#9: Tony Stark
My rule about versatility screws him over. When it comes to pure engineering, he’s basically on top of the list: have him work together with any other character in the top ten, and they can do anything. But when it comes to the truly absurd stuff… time travel, interdimensional tech… he’s not THE best. Although he probably thinks he is.
#8: Black Panther
Most likely below Stark’s level when it comes to engineering, but his versatility is way higher considering he knows physics as well as Reed Richards AND he’s learned a bit of magic as well.
#7: Valeria Richards
Reed’s daughter claims to be smarter than him. Maybe she’s right, or maybe her godfather Doctor Doom gave her more than her name. Either way, her youth (and her parents keeping an eye on her) is why she lacks enough feats to get any higher than this. 
#6: The Leader
I place him above Banner, Stark and T’Challa for building his own time machine, which in the Marvel Universe is a rare accomplishment.
He’ll definitely be surpassed by Valeria when she grows up, though. 
#5: Wizard
Wins major points in versatility, getting close to the technological level of Iron Man and Black Panther and even matching SOME of Reed’s technology. I place him above the Leader for having built a room that counteracts Scarlet Witch’s powers by “making probability random”, whatever the heck THAT means. I believe the Leader could build something that insane, but we haven’t seen it just yet.
#4: Blue Marvel
He tends to do his own thing in the books he’s starring, but lately he’s sometimes called in as one of the super-geniuses. Reed Richards is on record as calling him as smart as Doctor Doom, which I think is a bit too generous… but for a guy created in 2008, he’s worked fast at getting to the top.
#3: Hank Pym
Talk about being an expert at all things science. When it comes to biology, chemistry, physics and artificial intelligence, he’s either the best or a VERY close second.
There’s a reason he was chosen by Eternity himself as the Scientist Supreme! He could only lose to… 
#2: Reed Richards
THE super-genius of superheroes, PERIOD.
His track record is insane: he’s matched or more often surpassed anything done by every other person below on the list. But on top of THAT he’s the universal expert on interdimensional anything. No, scratch that, he’s LITERALLY the universal expert on anything science: there are entire alien species that come to ask for his help with science problems. Including several god-like ones. 
Reed Richards is undoubtedly THE greatest at science in the Marvel Universe… but I think there is ONE super-genius that beats him.
#1: Doctor Doom
That’s the cold irony about his rivalry with Mr. Fantastic. Reed doesn’t CARE if Victor is smarter!
And I would argue that Doom is a greater super-genius. He’s solved problems Reed couldn’t… save Susan during Valeria’s childbirth, but also cure the Thing or save the Multiverse in 2016’s Secret Wars. Plus Doom has a couple of advantages: he’s far ahead of Reed when it comes to both time travel, robots and artificial intelligence. That’s even before considering his knowledge of magic, which over the decades it’s come to rival Doctor Strange.
Unfortunately, the fact that Reed doesn’t feel inferior to him means Doom will never stop trying to prove himself superior. 