Dukat. I don’t like him a person, but he’s a great character. No other Trek character has ever been written as richly or layeredly as he.
At first you assume he’s your basic racist bent on hatred and power. Then you realize his obsession with Kira isn’t just about destroying an enemy, but his secret love-hate for Bajoran women. We meet Ziyal whom he mostly loves, but is ashamed of. He goes mad, starts a cult, makes himself appear Bajoran and starts a relationship with Kai Winn (ostensibly with other motives, but I think he reveled in it), and ultimately dies for and in his mad faith.
DS9 is lower on my list when I rank the various series, but some of the characters, and defininitely Dukat, top the list of characters.
Personally, I think it’s the best season so far, however the bar was not very high to start with. I wish Discovery started like this season, instead of the way it actually did.