I'm not particularly fond of most of them.

As many a voice already complained on this forum, mine included, Act3 is very much unfinished. Gortash in all honesty is a joke as a villain. He moves a lot of the pieces on the chessboard that is Baldur's Gate, but also completely overlooks himself, the king on the board. He admits that Orin - any Unholy Assassin of Bhaal really, Dark Urge included - are very good at their jobs and could easily assassinate him. Despite this revelation, he never makes an attempt to go underground and hide. He hides in his castle, surrounded by people... people who could be Orin? Any of them? Instead of holing up in a safe room with only the Steel Watch to guide him, machines that can detect invisibility? Nowhere near the efficient Tyrant that you'd expect the Chosen of Bane to be. In fact, Bane is the only God who just seems to be missing? You can interact with Bhaal and Myrkul, but not Bane - unless I missed Him completely. On my latest playthrough, I just straight up assassinated Gortash on the spot, and thats it, lol. No punishment or speech unlike with Myrkul or Bhaal.

The other one is Orin, although I mostly have an issue with her from the standpoint of how much of a pushover her bossfight is - aside the fact that unless you play Dark Urge, a lot of her characteristics can be lost on the players. But as for the fight, she's the only NPC in this game that can die in a Shapeshift effect - and please remember that the Slayer form is one of the most glass cannon shapeshifts. At least her death sparks a convo with Bhaal, but jesus christ Bhaal himself has to be the laughing stock among Gods to be one of many who have had their plains foiled because His children keep being idiots. Not to mention just how petty and underwhelming of a revenge He takes on a Good Urge.

Ketheric is the only person among the Dead Three who I actually respect as a villain. He is a force of nature and actually makes reasonable decisions as a leader. You get to observe and talk to him, and getting rid of him isn't as simple as stabbing him and moving on. He has his own motivations and goals with the Absolute plot, and catching him off guard by removing his invulnerability feels earned. His evil is palpable during all of Act2, and a lot of plot points end up to his demise, and it creates a massive payoff - where he becomes the Prophet of Myrkul, because as he said, he is willing to sacrifice anything to be with Isobel. My only issue is that if you play Dark Urge, he has dementia and never recognizes the Urge as the original Chosen of Bhaal, which is rather silly.