Dragon Ball Z introduced many new anime fans to the concept of power-scaling and over-the-top abilities. As such, any discussion, no matter how sophisticated or juvenile, about anime power levels will always come down to this question: can this character beat Goku from Dragon Ball Z?
Goku consistently breaks the in-universe limitations set for power to become increasingly mighty, to the point where reality buckles under the magnitude of his punches. However, Dragon Ball Z has limitations that other shows simply do not possess. As such, comparing Goku's power to, say, Sailor Moon's is ultimately a short-sighted question, since characters like Sailor Moon wouldn't fight Goku... they'd completely obliterate him! Magical girls don't follow rules like Goku does -- they create the rules. The following five magical girls could all easily defeat Goku.
Usagi Tsukino
Sailor Moon surpasses Goku's power in every way except for physical strength. Physically, Usagi is fairly weak, since she rarely engages in hand-to-hand combat. However, Sailor Moon's magical abilities are second to none. In her first arc, mere weeks after gaining her powers, she is able to harness the power of the Silver Crystal, a weapon that can obliterate planets. It took Goku years of training before he could develop that sort of power.
This is only compounded when you move onto the later arcs of Sailor Moon, especially in the manga. Usagi gains the ability to teleport across the universe without any restrictions, moving at speeds faster than light -- even faster than some of the transportation speeds the Gods take in Dragon Ball Super. Usagi can control the laws of reality, even being able to, at one point, destroy the source point of all the stars in the universe, effectively destroying all of reality itself. She takes on characters who can obliterate galaxies. This isn't even counting Sailor Cosmos, Usagi's future incarnation, who is essentially a God.
Snow White
Snow White from Magical Girl Raising Project is not as overtly powerful as many of the other opponents on this list. Her weapons include Princess Inferno's scimitar, a weapon so hot that all water evaporates immediately on contact. While this hot weapon could probably cause Goku injury, he has endured similarly hot attacks before. There is also Ruler, another halberd that is virtually indestructible. This could be used to parry any attack Goku issues, since, by its nature, it cannot be broken.
What makes Snow White such an effective counter to Goku is her ability to sense and understand the thoughts of any person she focuses on. As she develops her ability, she learns how to understand the fighting spirit of those who fight her. She uses this ability to determine what an adversary will do during a fight, and respond accordingly to counter that attack. This means that Snow White can evade any of Goku's attacks before he makes them. Whether or not she can move fast enough to avoid them or properly block them is a different matter, but this does mean that the playing field will be at least even.
Nanoha Takamachi
Nanoha from Magical Girl Lyrical Nanoha is an absurdly powerful soldier. Her abilities are augmented by her equipment and armor, but her Mana levels, according to official scales in the series, put her as one of the most powerful entities in her universe, period. This might seem impressive, but how does this scale to Goku?
Nanoha's abilities allow her to move at absurd speeds, deflect incoming bombardments and channel her mana into forces of destruction, but her strongest attack is Starlight Breaker. The spell allows Nanoha to recycle used up energy into a ball of pure energy, only to send it flying back at her opponent. This energy means that Nanoha and her opponent can both fight until the point of exhaustion, only for Nanoha to gather up expended energy on the battlefield -- including Goku's -- and send it back at Goku. In many regards, this is akin to Goku's own Spirit Bomb technique, but it takes far less time to charge up. An exhausted Goku would have to to endure the sum of his strongest attacks at once. His only shot? End the fight before Nanoha can use it.
Madoka
Madoka from Puella Magi Madoka Magica becomes a literal God. While she spends most of the series utterly powerless against the cosmic forces bringing ruination to her friends and companions, in the final episode, Madoka becomes a magical girl by making a single wish that literally bends all of reality. She elects to stop the cycle of witches entirely, which allows her to exist at all points throughout time, generating enough magical power to stave off the heat-death of the universe.
Madoka becomes capable of manipulating time, space, reality and energy, becoming ingrained into the fabric of her reality. She cannot be killed nor stopped... except, of course, by Homura, the "Satan" to her "God." In her God form, Madoka could destroy Goku. Because she is essentially the universe, there is little Goku could do to punch his way out of a fight with Madoka.
Sakura
Sakura from Cardcaptor Sakura could, in theory, beat Goku. Yes, she's a 12-year-old girl. She's not a God or military trained magical girl. However, Sakura's Clow Cards grant her such vast manipulation of space and time that Goku would be on the defensive for their entire bout.
The Time Card would allow Sakura to freeze Goku in time or force Goku to relive a time loop over and over again -- like throwing the same punch for eternity until his arm falls off. The Lock Card and The Maze could seal Goku away in an unbreakable maze. Then there's the Erase Card. This card would allow Sakura to just erase Goku from existence. No fight. No struggle. Just...gone. And Goku wouldn't be able to do a thing about it.