Zoro ''grandmaster'' Roronoa takes this for me, if anyone ate the badass badass no mi it is him.
Too stronk
Too much AP
Tsar Bomba
Here's a short list of pretenders but have no way to win against Zoro because of fewer appearance or instances of greatness :
Akainu ''hands in the pockets'' Sakazuki
Newgate ''dies standing'' Edward
Doflamingo ''Chad'' Donquixotte
Pedro ''the big balls''
Shanks ''Haki boy''
Some others I'm forgetting for sure but nothing like Zoro or at least not as much