While All Might is easily one of the biggest characters in My Hero Academia, he's still a small fish in the greater ocean that is anime. An industry famous for rivaling Western comics in terms of over-the-top powers and characters, anime has a long line of characters that can more than rival the brute strength and experience of Toshinori Yagi, aka All Might.
That isn't to say that All Might is a pushover either. Carrying the will and accumulated strengths of the One for All users, All Might has been able to clash with the monstrous Nomu, create massive wind storms with just a punch, and level entire city blocks. It's really saying something for manga and anime that there's a laundry list of characters that can push this guy around.
Master Roshi (Dragon Ball)
Master Roshi is most fondly remembered by the anime community at large as the vacationing old man who taught Goku a little-known, blue energy beam. For those who loyally stuck around the series all these years, Master Roshi has proven to be one of Dragon Ball's best fighters, through intergalactic epicness, has substantially stretched what a martial arts master is capable of.
While All Might has been able to punch craters in the ground and clash with the likes of All for One, Master Roshi has tossed around world-destroying threats and has even stood his ground against Goku. All Might's a good teacher, but he's nowhere near Roshi's level of epic, anime master.
Escanor (The Seven Deadly Sins)
Both All Might and Escanor have created the ultimate juxtaposition moments for anime transformations. For All Might, it was humbling to see such a proud and enormous hero shrivel up and become a sickly twig. Escanor's big debut is a considerable contrast from this. He premiered as a mild-mannered bartender who blew up like a balloon and easily defeated two overpowered villains.
And as funny as it would be to see quirkless All Might face off against a fully prideful Escanor, even All Might in his prime likely couldn't land a punch before Escanor would incinerate him. Escanor is just too fast, too strong, too "hot," and too prideful for even the #1 Hero.
Jiraiya (Naruto)
All Might in the Naruto universe would be seen as a marvel for taijutsu users, even by Rock Lee and Might Guy standards. However, as mighty and versatile as even the strongest taijutsu users have been in Naruto, they still don't hold a candle to the greater arsenals of some ninja masters, especially a sage.
While All Might could deal some damage from a pure, physical standpoint, Jiraiya is one of Naruto's most powerful characters and has the edge in every other area of combat and more. With his fighting skill, a wide array of ninjutsu, wide array of summonings, experience, and intelligence, Jiraiya doesn't even need to be in the same room as All Might to beat him.
Gildarts Clive (Fairy Tail)
Two heroes seen as beacons of hope and power for their respective proteges. Both are gilded in their respective histories for their accomplishments and both have sustained life-threatening injuries at the hands of endgame foes. If these two were to ever meet in a pub or the Fairy Tail bar, they'd likely have a lot to talk about.
However, while All Might's injuries have left him weaker, Gildarts Clive is still going strong with one hand. Even if All Might were at full strength, Gildarts has shown superhero speeds and the ability to pretty much dice anything with just a touch.
Dio Brando (JoJo's Bizarre Adventure)
As great and noble of a hero as All Might has been, he's still no match for some of the vilest and most treacherous villains ever to walk menacingly into anime. Few of those villains have ever been half as arch as JoJo's Bizarre Adventure's own, poster boy of cruelty and easily the best part of JoJo Part One, Dio Brando.
After All Might's most recent bout with All for One, one could believe that he'd be able to take on Dio in his base, vampire form, though Dio could still be a pretty, tricky guy. However, with the added bonus of being able to stop time with his stand, The World, Dio could accomplish what All for One wasn't able to.
Saitama (One-Punch Man)
Obviously, Saitama is stronger than All Might. With plenty of iconic scenes from One-Punch Man to look back to, Saitama is conceptually stronger than most fictional characters given that his entire gag is being able to defeat anyone with one punch. As mighty as All Might in his heyday has been portrayed, he's too grounded to ever face Saitama. However, it is interesting that these two characters in particular are constantly being compared to each other by the anime community at large.
While the anime world is diving more and more into interpreting Western-style superheroes, Saitama and All Might are both seen as the gold standards, just two different directions of looking at the power and stature that the idyllic superhero represents. Also, they both punch really hard.
Toriko (Toriko)
Well before Food Wars!, there was another anime series that blended together both culinary sensibilities and battle shonen writing. Toriko focuses on the titular gourmet hunter who scours the world looking for delectable food and ingredients.
And while this would appear to be just another Food Network series to the uninitiated, this series houses some of the most monstrous fighters ever seen in Shonen anime who have to be able to punch mountains and stop the world itself just to be able to wrestle their food. While All Might has dealt with relatively humanoid threats to save his city, Toriko has fended off apocalyptic monsters to protect the world and get a meal.
Whitebeard (One Piece)
During their respective debuts, All Might and Whitebeard were both two, generational standard-bearers who managed to stand tall despite being well past their prime. And while Whitebeard has likely sustained some battle scars (One Piece's old, pirate generation was wild), his biggest enemy towards the end of his pirating career was old age.
However, even hooked up to some IV posts and surrounded by nurses, Whitebeard was still a force to be reckoned with that could destroy massive buildings, split an island, and even summon tsunamis with just the flick of his hands. Given his title, All Might likely would've had to apprehend Whitebeard if the two ever had a crossover. Unfortunately, he'd be going into the fight of his life.
Kenshiro (Fist of the North Star)
There has been a subtle evolution within Shonen stories that has grounded its characters and storylines while still maintaining the genre's foundation on hard-hitting action. This isn't to suggest that old Shonen stories were poorly written but series like City Hunter and JoJo's Bizarre Adventure got away with a bunch of ridiculous stunts. That goes double for one of the genre's most iconic, action heroes, Kenshiro.
While he's famous within internet culture for being able to make heads explode with just a touch, Kenshiro has proven to be pretty durable against immensely strong foes, and quick enough to deal hundreds of finishing blows before his opponent can even take a breath. While All Might certainly delivers in strength feats, Kenshiro never needed much than just an opening to deliver a finishing blow.
Arale (Dr. Slump)
There are plenty of characters from the Dragon Ball multiverse to pit All Might against (and inevitably see squash him). However, one of the most definitive mismatches against All Might and one of the most powerful anime characters of all time comes from another Akira Toriyama series. Arale is a cute, spunky little girl who loves learning about the world around her and making friends.
However, she just has a small issue with containing the vast amount of strength given to her by the scientist Senbei Norimaki. A robot of Dragon Ball proportions, Arale is a spectacular piece of machinery that can split the Earth in two with just a chop. A little harder to handle than Eri, Arale could be a real threat to the My Hero Academia world.