Luffy and Boa Sandersonia.

Absolutely, one of the smallest but most defining moments to show how Luffy thinks about conflicts. For me, I think Zoro's sacrifice for the crew was a highlight for me, I still remember having to wait to find out if he survived or not buy taking Luffy's pain. Usopp's apology, Chopper's backstory, Rob Lucci fight... man so many great moments. But I do agree with you, Oda build Impel Down and the war it was such an epic moment of the series.