The most common answer will be Sanji as we've foreseen a scene in Wano where Oda has teased us with evil Sanji, this could be the perfect scenario, but how strong will he be even if gets buff by IMU? From YC1 to low top tier maybe, but will that be even a threat against the likes of ACOC monsters like Zoro, Loki and Luffy? no
Instead, it shall be Loki, and Luffy will need to defeat Loki to parallel Shanks
Instead, it shall be Loki, and Luffy will need to defeat Loki to parallel Shanks

