For example, in Harry Potter and the Deathly Hallows – Part 2, Snape was reluctant to fight McGonagall when the latter took him to a duel in front of Hogwarts students. Both characters had their strengths, but the last Harry Potter movie proved Snape was the strongest Hogwarts professor.
Hands-down, Albus Dumbledore was the most powerful wizard of his time. Most regarded him as the strongest wizard in history, and even Lord Voldemort himself feared to face him. Beyond his many impressive titles and positions of power, Dumbledore exhibited absolutely extraordinary abilities on several occasions.
Godrick Gryffindor, one of the four founders of Hogwarts, and the owner of the legendary Sword of Gryffindor, was absolutely more powerful than Dumbledore— and it's a good thing he was, too, because Dumbledore wasn't around in Hogwarts' early days to keep Godrick's fellow founder Salazar Slytherin in check.
Formerly known as Tom Marvolo Riddle, Lord Voldemort was the most formidable evil wizard in the entire universe. Until Harry Potter, Voldemort's magical prowess was practically unmatched, and no one could stand a chance against him.
1 Lord Voldemort
Considered the most powerful dark wizard of all time, Voldemort was obsessed with his own half-blood ancestry and his search for power and immortality. To achieve the latter, he used his enemies' murders to fracture his soul into six and create his own set of Horcruxes.
[Harry Potter] Voldemort was more powerful than Dumbledore; Dumbledore was more powerful than Grindlewald. In some of the backstory of the Harry Potter books we learn that Dumbledore acquired the Elder Wand by defeating Grindlewald in a duel.
Gandalf is greater than Dumbledore, although (or perhaps because) he had less power. He rallied all the free peoples of Middle-Earth to the cause, gave them heart, and sacrificed himself to save his friends and the quest in Moria. He worked tirelessly for centuries.
Minerva had mastered the Patronus Charm, being able to create a powerful corporeal Patronus in the form of a cat — identical to her Animagus — , being the only person seen to cast three Patronuses at once. She also was able to use her Patronus as a means of communication, as taught to her by Dumbledore.
Following Lord Voldemort's defeat at the hands of her student Harry Potter and the deaths of Headmasters Albus Dumbledore and Severus Snape, McGonagall takes the position of Headmistress.
Gellert Grindelwald was basically the Adolf Hitler of the wizarding world, but he also happened to be Albus Dumbledore's closest friend.
Winner: Snape
The kind of versatility in magical abilities that Snape displayed was almost around the level of Albus Dumbledore and Voldemort, making him easily more powerful than the average wizard and even the members of the Order of the Phoenix and the Death Eaters.
Severus Snape might have pretended to serve Voldemort (while in fact, as we all know, working as a double agent for Dumbledore), but there's almost no question he was more powerful than the Dark Lord.
Weaknesses. McGonagall is never portrayed as having any particular weaknesses. Her stern facade likely prevents anyone from getting close to her emotionally, with the possible exception of Dumbledore. We are led to believe that she prefers her solitude.
Albus Dumbledore is the most obvious person who can defeat Voldemort, and the Dark Lord seemed to realize it. Rowling herself has explicitly stated in the books that Dumbledore is the only person Voldemort fears and recognizes as a genuine threat to his own power.
Given that the third film takes place in the early 1930s, we still have a little over a decade to go until the legendary duel in 1945 that netted Albus the Elder Wand (one of the Deathly Hallows) and saw Grindelwald trapped in his own castle until he was murdered by Voldemort years later.
Dumbledore almost certainly. Snape is a good duelist in my opinion but definitely a cut below the three powerhouses of the series. Dumbledore's age doesn't have any of the comventional drawbacks from what we've seen in Half-Blood Prince.
He may be the titular character, but Harry is far from the most powerful wizard in the wizarding world. Sure, he does eventually go on to take down the greatest dark wizard of all time, but his success comes more as a result of his mother's sacrifice and the support of his friends than it does his own brilliance.
Throughout the Harry Potter series, Albus Dumbledore, the beloved Headmaster of Hogwarts, proved time and time again that he was the smartest hero of the Wizarding World. His magic was so strong and his knowledge so extensive that he was the only wizard Voldemort was said to be afraid of.
Grindelwald Is More Powerful and Cunning Than Voldemort
Grindelwald had more power in the Wizarding World up till the final moments of his life. He had more followers, and they were intensely loyal to him. He conquered more of the globe and could perform more advanced forms of magic.