I love the Mustafar lightsaber duel.
If there’s one lightsaber duel everyone seems to love but I personally think is the most overrated, it would be the one between Obi-Wan and Qui-Gon vs Darth Maul, way too choreographed.
If I had to pick an all-time favourite lightsaber duel, it would be Anakin and Obi-Wan vs Dooku in RotS. It’s brief, simple and elegantly choreographed.