Sanji's speech to Usopp about everyone having a role on the crew and each of them making up for the limitations of the other. Really great after Usopp continued to have doubts about himself due to losing in physical confrontations and feeling weak. Also worked because Sanji, himself, was a liability at times so he had to depend on Nami (to face Kalifa earlier) and Usopp (to save Robin with his sharpshooting at that point in the arc) to accomplish what he wasn't capable of and instead he handles Jyabura which was something beyond Usopp so it really worked with the themes of the arc, revolving around trusting your crew and accepting each other's faults.
Whitebeard's speech at the end of Marineford about One Piece existing was great and still gives me goosebumps when I rewatch it. Zoro's speech to Luffy about the rest of the crew having to respect Luffy and Luffy needing to be resolute and decisive in his decisions was also really good and it's one of the reasons Water 7 was such a great arc and one of the most memorable.
"Don't try to find a reason for somebody's love" - Sengoku
"Maybe nothing in this world happens by accident. As everything happens for a reason, our destiny slowly takes form." - Rayleigh
"You guys are fired." - Zoro
"It's not a devil fruit or some cheap trick... one by one, he turns the people around him into his allies. More than anyone else sailing the seas... that man possesses the most terrifying power." - Mihawk
"Be careful on your way." - Mihawk
"What a shame... Just what are you reminiscing about... that's caused you to weep like that, brother? If we ever cross paths again, tell me that story, over a drink or two." - Franky