Honestly? Kaguya.
Madara was a warmongering psychopath, I didn't even understand why he wanted "peace" when he was sporting an erection during the entire war arc. Nothing was effective against him, either. He undersold everything, made stuff up as he went along, and just kept degrading and humiliating everyone he saw. Anti-climatic and boring.
Kaguya may seem entirely new, but her story is intertwined with Hagoromo, Shinju, Black Zetsu, Ashura, and Indra which gives her depth while she's slowly gaining character development. Her abilities have so far also been more interesting; hell, Juubito seemed more menacing and overwhelming than Juudara. With Obito, I had a sense of "How are they going to beat him?" With Madara, I had a sense of "When are they going to beat him?"