you really think Chopper is fighting Queen he just attacked him while Marco was holding him.
and as you see Marco is busy holding Queen which makes King free so he can go after Momo, Sanji might have to begin his fight against King soon. i am not fixated on that he could fight Queen as well. Jack is least possible option though for many reasons like there is a character with scabbards who might be strong , and the scabbards will be able to defend themselves , and even Tobiroppo according to Jack himself should not be able to finish them off, and they have a gurdge against Jack since he is the one who attacked Zoo and fought them on the roof as well. so they really should be the ones who finish him off at least that since they were not able to do anything against Kaido