Originally Posted by
Augury
Speculation is made on this subject will all have a weak base since we haven't seen anything substantial from the above mentioned candidates. How to be recognized as the Pirate King isn't even spelled out clearly. In my opinion the answer should be left at "one of the four emperors," but I'll have a go at it anyways:
What we know:
1. Roger was the Pirate King and left his treasure, One Piece, "there."
Common Assumptions:
1. One Piece is a tangible object at the last island in the Grand Line, Raftel.
2. Obtaining One Piece is a prerequisite for being the Pirate King
3. Obtaining One Piece is related to a pirate's power
Following this line of thought, the question really almost devolves into another "who is stronger?" type of thread which doesn't really have an answer.
I think there are areas that should be looked at (aka the assumptions may be flawed)
1. Is One Piece necessary for being the Pirate King? We don't know the world's status 22 years ago nor Roger's situation relative to his rivals. Being the Pirate King could be something more intuitive, such as decisively controlling the New World.
2. As some people have stated, there hasn't been a Pirate King for over 20 years, so succession is difficult for one reason or another. If this is related to controlling the seas, then the power question comes in... but if it is related to obtaining One Piece, there could be other barriers. Some theories I've heard are extreme high / low tides or poneglyph-related keys.
3. I think the power-only approach is incorrect, since Oda has placed Whitebeard's past power on par with Roger's. After Roger's execution, common sense logic would follow that someone with the same "level" of power would be able to accomplish the same amount of domination if that was the only thing that was needed.
Bottom line: There isn't enough overall information, and common underlying assumptions are most likely incorrect.