My first favorite moment for Usagi is when she kills the possessed Tuxedo Kamen. Yes that's my first favorite. I know it seems skewed, but allow me to explain. Usagi loved Mamoru, there really isn't much question about that. Sure he was evil at the time and tried to kill her, but you know that could never weaken her feelings for him. As she realizes he cannot change back and the end the fighting, she must be decide between her love and her duty. And she choose duty. There is nothing more she could have done to earn my respect more.
Another of my favorite moments is when she tries to stand up against the outer senshi when they announce that they intend to kill Hotaru. Her shock shows what a truly good person she is. Even when Hotaru as Mistress 9 steals Chibi Usa's crystal and it puts her in life threatening danger, Usagi still seeks to save Hotaru.
When Saturn did her magnificent Death Reborn Revolution to destroy the world, it was up to the power of Super Sailor Moon to save the world. She truly became the messiah and saved the world and baby Hotaru too.
When she was confronted by Lethe and Mnemosyne and Lethe told her that her very power and existance created these wars Eternal Sailor Moon offered to die to end the wars. She truly meant it and this showed her true dedication for peace.
In the final battle, she gave up her life and descended into to Cauldron to save the world once again. Her speech was beautiful and once again this shows my attraction to devotion to duty.