Like Big Mom and Kaido, Whitebeard was also one of the pirates on Rocks' ship. After the God Valley Incident, however, he created his own crew, known as the Whitebeard Pirates, and became one of the strongest pirates out there. At some point, Whitebeard became the strongest man in the world.
Over the years, he acquired a bounty of 5,046,000,000 berries, which was the highest known active reward until the Paramount War, two years before the current storyline.
Undoubtedly, the biggest weapon up Whitebeard's sleeve was the Gura Gura no Mi, the strongest known Paramecia-type Devil Fruit. With its powers, Whitebeard could create quakes at will and lift the entire ocean against his enemies. Whitebeard's power was once labeled to be strong enough to destroy the entire world.
Out of all the pirates in the One Piece world, Whitebeard is the only man who could match Gol D. Roger in a fight, making him the strongest Yonko.
With the Gura Gura no Mi, Whitebeard had the power to destroy the world, but he also had other abilities at his disposal that made him as menacing as he was. In his prime, Whitebeard had access to advanced Haki types in Armament and Conqueror's Haki.
In his clash against Roger, fans saw how the two matched each other in battle. Whitebeard also possessed the Murakumogiri, a Saijo o Wazamono grade weapon, to aid him in battle. Without a doubt, he was incredibly versatile in combat.
The man known to be the strongest creature, Kaido is widely known to be the most powerful pirate right now, and the mightiest of all Yonko currently. He was an apprentice on Rocks D. Xebec's ship long ago and he was given his Devil Fruit by Big Mom on God Valley.
Since then, Kaido has continued to grow stronger. His actions have earned him a bounty of 4,611,100,000 berries, which is the highest of any active pirate in the story.
Kaido is an unbelievably powerful fighter on his own but his reputation of being unkillable and his immense durability come from his Devil Fruit. 38 years ago, on God Valley, Big Mom saved Kaido by giving him the Uo Uo no Mi, Model: Seiryu.
This Devil Fruit, being a Mythical Zoan, allows Kaido to transform into a mythical eastern dragon and its hybrid at will.
Kaido's Mythical Zoan fruit has given him the power to train harder and grow stronger. As such, Kaido is extremely balanced across all the fields of combat, be it Devil Fruit usage, or Haki.
Kaido possesses incredibly powerful Haki and he can make use of all the three advanced forms of it. His strongest Haki ability is certainly his Conqueror's Haki, using which he launches some of his strongest attacks such as Thunder Bagua.
Charlotte Linlin, also known as Big Mom, was a natural-born destroyer. At the age of 5, she was powerful enough to kill the former captain of the Giant Pirates, Jorul, with a single throw. With time, Big Mom got even stronger and by adulthood, she's become one of the fiercest pirates on the seas at the moment.
With skin as hard as iron and strength that is enough to defeat most characters in a single blow, Big Mom is every bit as monstrous as Kaido, as is evident from her 4,388,000,000 berry bounty.
Big Mom is fairly balanced when it comes to her abilities as a Yonko. Not only does she use her Haki incredibly well, but she's also a great user of her Devil Fruit power. That said, Big Mom does rely more on her Devil Fruit which means it is her strongest power. The Soru Soru no Mi allows her to control souls freely.
Big Mom can freely give life to any animate or inanimate object using her power. She can also take anyone's lifespan away with ease. Those who are even the slightest bit afraid of her don't stand a chance against her.
Big Mom makes use of her Soru Soru no Mi the most in battle, however, she has many other powers up her sleeve. For one, Big Mom has a tremendously powerful Haki. She can make use of the advanced forms of both Armament and Conqueror's Haki, as seen in her showing throughout the Onigashima War.
At the same time, Big Mom is also built like an iron fortress, meaning she is impossibly hard to damage from the outside.
Shanks is another recent addition to the ranks of the Yonko. He joined the group six years before the current storyline and immediately became one of the strongest pirates on the seas. Shanks has a bounty of 4,048,900,000 berries on his head, which he managed to acquire in a very short period of time.
Shanks was powerful enough to stop Kaido from attacking Whitebeard before the Paramount War and could clash with Newgate himself on an equal footing.
Unlike the other Yonko, Shanks isn't a user of any Devil Fruit power. Instead, he relies solely on Haki in combat. Given that Shanks is a user of Conqueror's Haki, his biggest power in combat is this very skill.
Shanks' Haki was praised by Diamond Jozu, Whitebeard's Commander, and Whitebeard himself. Shanks is most certainly capable of infusing his attacks with Conqueror's Haki and taking down most of his enemies.
Shanks is a proficient user of Haki and thus most of his powers are built around that ability. Shanks possesses the ability to use all three types of Haki. While he undoubtedly possesses great control over Conqueror's Haki, his Armament Haki and Observation Haki are likely going to be very advanced as well.
At the same time, Shanks also wields Gryphon, which could very well be one of the Saijo o Wazamono grade swords.
Marshall D. Teach, also known as Blackbeard, became one of the Yonko only recently in the story. After the death of Whitebeard, Teach fought for supremacy in the New World. He managed to defeat the Whitebeard Pirates, led by Marco the Phoenix, in the Grudge War following which he became one of the Yonko.
Currently, Blackbeard has a bounty of 2,247,600,000 berries on his head, making him the Yonko with the lowest reward. With his two Devil Fruits, Teach is nigh unstoppable in combat.
Without a doubt, the biggest aces up Teach's sleeve are his Devil Fruit powers. During his time with the Whitebeard Pirates, he managed to steal the Yami Yami no Mi from Thatch, followed by the Gura Gura no Mi from Whitebeard after killing him on Marineford.
With the power of darkness, Teach can suck in everything, including light itself, while the Gura Gura no Mi lets him create quakes with the power to level islands with ease.
Out of all the Yonko, Blackbeard most likely has the shortest set of skills. His two Devil Fruits are his biggest assets, but, other than that, fans don't know much about what he's capable of. Blackbeard does, however, have the ability to use both Armament and Observation Haki.
Whether or not he has Conqueror's Haki remains to be seen. At the same time, he is incredibly resilient and can take a lot of damage, something that even Marco called special.