The fight that impressed me the most was the Ryuma vs Zoro. It was the first time that I saw so much good choreography in a sword battle in One Piece !
Furthermore, I felt that the fight was effectively well balanced between the two : there was never a period when there was one who dominated the other more, they surrendered blow for blow which has resulted in a very intense duel (no pause for an introspective monologue or for a useless conversation, just FIGHTING

).
In the end, it was the advantage of the ground that gave Zoro the opportunity to take the upper hand over Ryuma (which shows that he too has a very good tactical sense, he also showed that against Pica and against the Gifters when Luffy was knocked out by Apoo).
It really felt like a fight you can see in real life. It was very realistic and that's mostly why I think I particularly enjoyed this fight more than any other.
Now that I think about it, I don't remember if there was another One Piece fight with such good choreography and realism
