Obviously Katakuri for me. The first villain in the entire series who was given character development in the same arc/main fight (him abandoning his perfect brother persona, acknowledging and respecting his enemy (which was not shown with previous villains, they started to respect and acknowledge Luffy either in later arcs or they simply didn’t), clashing with the main character due to the reasons different than greed, being in control etc.). No wonder he was the first villain Luffy showed outright respect to, he simply wasn’t an evil arc enemy. Moreover, he was, in many ways, the best opponent Luffy could ever have. The way he utilized Mochi Mochi no Mi, Logia like powers with range and stickiness, seemed like superior version of Gomu Gomu no Mi in certain aspects (even though the foundations of fruits are different, I am talking application wise), his superior Haki, awakening etc. He is more than a arc boss in the series, a dynamic character open to development from many perspectives. We will probably see him in following arcs and the final war.
Second for me is Queen. He is a funny character with many personality quirks :D