We are not sure about many of their ambitions but... Imu is the most influential being of the world but still doesn't controls everything and it seems to be moving towards that. So yes he is top of the top.
Teach seems to me similar? Although in a more free way. So like Rocks he would be right after.
Then we'd have Kaido that doesn't necessarily wants to control the world but wants to put it into a huge war, only to make violence. For no reason at all. Since his personality has no deepness.
Then I'd go with Big Mom that made a HUGE family and uses it to force marriages to make herself stronger both political and army wise but in reality we don't know what she wants despite being Pirate Queen. But for what reason? What she does next?
Then Whitebeard the lonely old man who just wants a family so he doesn't dies alone.
Then Roger who just wants to travel around the world.
Then Luffy because he is too dump and just wants it because he thinks he can't be the most free person if he is not the pirate king.
Then Shanks because we don't know what he wants.
But that's based on your list.
My list would be
- Imu
- Rocks
- Teach
- Crocodile
- Doflamingo
- Zoro
- Mihawk
- Harald
- Buggy
I'd put Ryuuma between Crocodile and Buggy.
Explanation: Imu, Rocks, Teach wants worldwide domination. Imu more controlled. Teach more freedom. Rocks I'm betting to be a mid term between them.
Crocodile we are not sure but it feels like he probably has worldwide domination ambitions as well.
Doflamingo was fine by controling the subworld.
Zoro and Mihawk just wants to be the best. Mihawk wants a real challenge. Zoro wants to be the best in history.
Harald and Ryuuma seems to just want to protect their nations.
Buggy just wants to get rich.