You answer your question yourself, it is Luffy.
I understand it's hard to accept, but as you might have noticed Queen has a lot of links with everyone who is currently on the live floor.
He promised to torture Drake and he attempted to kill Apoo and Chopper. Many pleasures and waiters there hates him.
Chopper has an insane amount of reasons to fight him, even connected to his dream, and Queen and Perospero are basically his only possible opponents. But he slapped Queen in the chapter dedicated to him and Brook should be the one avenging Pedro.
At a certain point, i was sure Sanji was going to fight Queen too and perhaps Oda was willing to draw that too. But chapter after chapter it became less and less likely.
Drake's plotline, Sanji clashing with King, King obsession on killing Momo and the scabbards and Sanji's one to save them, their fighting style, then Chopper and Apoo. Queen and Sanji have been pushed further and further.
Except for two thing:
1) Queen using technological advances weapons to fight.
2) Queen mentioning Judge
But how is Queen and Sanji using technology to fight more relevant than King and Sanji both flying and using fire?
Queen mentioned Judge, but they are both scientists, of course he knows him. We even got the confirmation Kaido was captured by Vegapunk, and Judge was his coworker. It wouldn't be hard to make Judge and Queen appear in Kaido's flashback working in the same team.
Why does a potential link weight more than actual attempts to kill somebody (Drake, Apoo and Chopper) ?