Changing my vote to Hancock. By her own admission, she can't stay in Amazon Lily or the Marines will keep attacking, and her stated solution is to go and be with Luffy. At the very moment she decides this, the former empress/captain shows up on the island out of nowhere to be her replacement. And on top of that, Yamato being a red herring for Hancock makes 1000% more sense than her being a red herring for Carrot. Not to mention we already know she has a tragic backstory that hasn't been shown yet. She could even have a role, ironically, as beast tamer, bringing along serpents like the ones on the Kuja ship so the Sunny can travel in the calm belt, allowing them to easilly return to previous islands like Wano, Alabasta, Saboady/Maryjois, and Fishman island.