The power you are born with is the power you keep. Hermione, however, is one of the few characters who achieves great skill mostly through hard work. She edges out many other strong characters in Harry Potter due to her prodigious work ethic, friendship, and ability to get even more powerful overtime.
Hermione Granger
To her credit, Hermione is capable of advanced spells beyond her years, and she knows when and where to cast them. However, fighting another wizard is different from charming or transfiguring an object, and if Harry really wanted to, he could overpower Hermione in a serious duel.
Hermione could beat Dumbledore any day if she wanted to. She's one of the most brilliant minds of her generation; like any good Gryffindor, she's brave, loyal, and strong. She mastered advanced spells at a young age, could make any potion perfectly, and her quick thinking saved her, Ron, and Harry more than once.
Hermione Granger is the "cleverest witch of [her] age" and the strongest Hogwarts student in the series. Harry and Ron are deeply proud of their friend's prodigious skill and genius intellect, often relying on her intuition to save the day.
Hermione Granger
Beyond just being studious, she was able to perform extremely advanced magic, like brewing the Polyjuice Potion as a second-year or the combination Protean Charm/jinx on Dumbledore's Army's coins that permanently disfigured classmate, Marietta Edgecombe.
She is also the first one of her age to be able to cast non-verbal spells. Hermione is a competent duellist – Rowling has stated that during the first three books Hermione could have beaten Harry in any magical duel, but by the fourth book Harry had become so good at DADA that he would have defeated Hermione.
Albus Percival Wulfric Brian Dumbledore was the only wizard Voldemort ever feared and the only one who could have defeated him in a duel. Albus Dumbledore is the most powerful wizard in the Harry Potter.
Ginny and Hermione each have their own strengths. For Hermione, she's logical, book smart, and clever. Ginny is smart too, but in other ways. She's more kinesthetic and she's a gifted Quidditch player.
Dumbledore also said that Voldemort was probably the most brilliant student Hogwarts has ever seen. Although Voldemort remains highly accomplished and prodigious in skill, he is enormously lacking and highly inept in the most powerful magic, love.
Tom Riddle/Voldemort
Professor Dumbledore once said that Tom Riddle, a.k.a. Lord Voldemort, a.k.a. "He Who Must Not Be Named" (Ralph Fiennes/Hero Fiennes Tiffin/Christian Coulson), was the most brilliant student that Hogwarts has ever known.
So when Voldemort still has his horcruxes and Hermione is the oldest we know her to be 17 in the final book. If they dueled, Hermione would have lost. Tom Riddle or Voldemomort has d too much experience and knowledge when it came to spells and the dark arts. However Hermione was comparatively experienced as a child.
Godric Gryffindor, the founder of Gryffindor house, was one of the most powerful wizards of his age, so powerful that he was said to be the greatest duelist of that era. Always ready for battle, Godric wouldn't just use a simple wand, he'd also wield a mighty sword.
She is a powerful witch with abilities rooted in her strength, determination, and fortitude. Early in the series, Hermione established herself as a force to be reckoned with, but when push comes to shove, she wasn't near the level of skill needed to defeat the likes of Bellatrix Lestrange.
Harry: Better At Defense Against The Dark Arts
In the books, Harry's O.W.L. results for DADA are higher than Hermione's, the only exam in which he outperformed her. His defensive abilities are an asset for the young wizard that gives him an edge over his best friend in combat.
The most powerful muggle is Mary Lou Barebone from the Harry Potter spin-off Fantastic Beasts and Where to Find Them. As the leader of the New Salem Philanthropic Society (aka the Second Salemers), she holds an immense amount of power as she attempts to bring down all witches and wizards for good.
Harry also happened to be Snape's least favorite student.
J.K. Rowling once explained that Ginny Weasley is so powerful because she is the seventh child of a seventh child. This is part of folklore that has been around for a long time.
As the youngest Weasley, we're sure Ginny observed more than her fair share of unpleasant spells over the years but it was the Bat Bogey Hex she was famous for – and with good reason. This was the spell that overpowered Draco Malfoy and the Inquisitorial Squad, and also secured her an invite to the Slug Club.
It shouldn't be hard to believe, but Draco Malfoy was the second most intelligent student in all of Harry's year. That Slytherin determination can accomplish quite a lot. Draco received at least three OWLs (including both Transfiguration and Potions) and he is very competitive with Hermione.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
While most fans agree that Harry is the unrefuted Chosen One, the final Deathly Hallows film (in particular) sways heavily toward highlighting a heroic Neville, revitalizing the debate regarding which boy is better suited for the iconic title. "The one with the power to vanquish the Dark Lord approaches ...
The most powerful wand in the entire Harry Potter universe is the Elder wand — one of the three Deathly Hallows. Made out of the tail hair of a Thestral, the wand can only be handled by the strongest of wizards. Made by Death itself, the wand can be used with the other Deathly Hallows to make one the master of Death.