Obi-Wan Kenobi vs. Anakin Skywalker (Revenge of the Sith)
This lightsaber duel played a pivotal role in setting up the events of the original trilogy as it served to explain why Anakin was forced to make his full transformation into Darth Vader.
This battle not only featured the most exciting lightsaber choreography, but it was also full of emotions as Obi-Wan was forced to confront the man he thought of like his brother, yet he had to look past who he formerly was and realize he was a dangerous threat to the galaxy that had to be stopped.
The duel was set up emotionally as Padme and Obi-Wan arrived on Mustafar to try and stop Anakin. After Anakin force-chokes Padme to the point of unconsciousness, some of the best dialogue in the entire prequel trilogy is delivered between Obi-Wan and Anakin as Obi-Wan tries to talk him off the edge.
Obi-Wan exuded clear sadness and pain after subduing Anakin as he laid on the ground screaming in pain, agony, and hatred. The former Jedi was supposed to fulfill the prophecy as the Chosen One and bring balance to the Force, yet Anakin chose a different route which led to the near-extinction of the Jedi.
Obi-Wan projected evident sadness as he spoke his final words to his former Padawan, saying, “you were my brother, Anakin. I loved you.” With this, all remnants of Anakin Skywalker were left behind as the Chosen One was forced to take on the persona of Darth Vader.
This duel served as a near-perfect segue to transition the story from the prequel trilogy to the original trilogy and did an excellent job of bringing everything full circle.