The top 10 unknown bounties in One Piece is a totally guessed top linked with the material we already have from One Piece.
Permanent member of the revolutionary army, fighting as the right hand of the "most wanted man", he helped Luffy to defeat Do Flamingo in dressrosa and in addition he obtain the mera mera no fruit than Ace was used before. Adoptive brother of Luffy and Ace, he has probably a bounty on his head at the same level than them.
Even if Rayleigh is retired, he still appeared active by bringing Luffy's strenght at another level during the 2 years time lapse. Former member of Gold D.Roger's crew., skilled fighter.
As a shichibukai, the potential bounty of Dracule Mihawk is frozen. We can consider this last one as very high due to the fact he is a lonely Pirate contrary to others shichibukai, and he is already considered as one the best swordsman in the world, which let to think than there are proofs in the past about how strong he is. Knowing than Akagame Shanks is also a swordsman, and than he was easily able to be the master of Zoro.
Whitebeard Edward Nerwille
He has no bounty anymore as he died but Shirohige was one of the Yonko and his impressive strenght bring him to fight against all the marines.
Gold D. Roger
The old infamous king of Pirate, executed in Marine Ford, and the only one to visit the last island Raftel where he has hidden his treasure, the One Piece.
Kaido the beast is considered to be one of the strongest character in One Piece, and probably the strongest using only physical force. His right hand Jack showed his bestiality, and already have a bounty of 1,000,000,000 berries on his head. We can guess than the terrific Kaido, unable to die, arrested 18 times, should be valuated at minimum the double. He is the only character than the bounty show 'only die'.
Having three of her commanders with bounties around 1,000,000,000 berries already, Big Mom is a terrific character able to control the souls of people thanks to her devil fruit. At the head of a large family, she built alliance with several Pirates. She is able to destroy cities, and islands, just because she is hungry.
Hard to say how much is valuated the bounty of Blackbeard. Terrible Pirate who became one of the strongest character in One Piece, he fought against the old crew of Shirohige ( Whitebeard ) to gain a position as a Yonko. We know than he has a bounty of 0 berry when he was a Shichibukai, in despite he has been one of the former member of Gold D.Roger's crew.
Former Pirate in the Gold D.Roger crew, he is now one of the four Yonkos. Even if no one really know how powerful he is, he stopped the war in Marineford by requesting it, and the world government didn't intend to fight anymore with his entrance, and Blackbeard himself decided to leave.
Monkey D. Dragon
Known as "the most wanted man in the world", Monkey D. Dragon is the leader of revolutionary army and aim to destroy the world government. Son of Garp, and father of Monkey D. Luffy. Very surely the highest bounty in the world of One Piece.