Just a few of my thoughts on the choices on the poll:
Aokiji - Would be a dope opponent for Sanji but Oda is never gonna match Sanji up against Aokiji, simply bcoz there's just no way to establish Shiryu above him unless the latter beats him on panel which is very unlikely to happen. At the very best we see Shiryu and someone else team up against Aokiji to beat him.
Burgess - From the perspective of prominence in the BB pirates, he's qualified enough to be Sanji's opponent however Burgess is way to simplistic to be Sanji's opponent in the BB Pirates. Sanji's opponents are usually tricky/hax types (i.e. Bentham, Absalom, Queen etc.) that put him at some sort of disadvantage in his fight and Burgess is the polar opposite of that. Closest ting we've gotten to direct opponent we've had matched up against Sanji in recent years is Jyabura and he still somewhat fits the tricky category.
Vasco - Not sure why he's so popular recently but out of all the BB Pirates, he has the least panel time alongside Sanjuan Wolf which should really tell u all u need to know with regards to his chances of being Sanji's opponent.
Pizarro - Second most likely candidate on the list imo, simply bcoz of the North Blue connection he has with Sanji and also an inkling that he could potential fit the tricky opponent category.
Laffite - Most likely to be Sanji's opponent from a prominence and portrayal perspective, even more so than Burgess (i.e. 1.) was tasked with the responsibility of invading Marijoea pre-ts to recommend Teach as Shichibukai, 2.) put Pizarro in his place when the latter stated that he was going to try to take Teach's seat as Captain, 3.) only BB Pirate that wasn't embarrassed by Ace on Banarro Island, 4.) the Chief of Staff of the Blackbeard Pirates pre-ts and still holds said title even now, 5.) his initial design is the most intriguing out of all of BB's commanders as BB went out of his way to recruit him from what seemed like WB's crew and not even as a subordinate but as a partner). In addition, he's also able to to use hypnosis which makes a him a tricky opponent by default so he fits the bill for a Sanji type opponent. Then there's the fact that he's in possession of a flight zoan which is very rare and usually possessed by the most prominent members of different organizations (e.g. Pell, King, Marco)
Out of all the guys on that list, none even come close to Laffite as a prospective opponent for Sanji imo.