IMO:
WB
BB
Unknown Yonkou OR the yonkou shanks is currently fighting
Shanks
Unknown Yonkou OR the yonkou shanks is currently fighting
Dont get me wrong, im a huge shanks fan. But there is no way he can go up against whitebeard, he can challenge him and argue with him. And he's powerfull enough to keep WB at bay!
WB is currently the strongest one, there is no reason why he shouldnt be. Whitebeard is number one, FOR NOW! Remember this one, he is destined to loose his spot somehow!
Then there is BB, allready before he got the Devils fruit he was powerfull enough to take on Shanks himself! It's frigging ridicilous to hear people underestimate him time after time, BEFORE he got the devils fruit god dammit. And the most powerfull devils fruit in the world at that, the one he had been hunting for all his life! BB might even be more powerfull then WB is, perhaps he will show us just that in the duration of this arc!
Then there is the unknown Yonkou, I believe he is more powerfull then Shanks simply because they couldnt reveal a weaker Yonkou then the previous ones last. Perhaps the allready revealed "halfway" by face Yonkou is the secound strongest though.
Shanks, he holds both power and respect! I believe him to be the third most powerfull of the pirates. He's allso a Peace Main, aka a pirate that doesnt rob civilians and all of that shit! But fights for what is right, thats why I believe him to be third. Simply because Whitebeard if the "famous" one, Shanks is the Peace Main, and then there should be one inbetween them which is a terrible guy we all hate!
Last Yonkou comes last because Shanks cant!

Oda would never do anything like say "Shanks is the weakest of the Yonkou".
But stop bullshitting about BB, he's up there with the Yonkou EASELY. Might even be on top!