I don't like Maeve but my god she's a good villain. She's awful, heinous and motivated by nothing but her own interests. How she treats others, especially those under her power is beyond horrific. I'm a little scared of Sarah J Maas for creating her honestly, especially after Tower of Dawn...
AIDAN. The creepiest and most murder-y AI to have ever existed. I think what makes him so terrifying is he truly believed he was doing the best thing for his people. That the mass death was necessary in order for the rest of his people to survive. That and you could never guess what he was going to do next, or if he was friend or foe.
The Jackal. Another creepy, awful and plain nasty. He's the perfect villain. Think a little like the Joker, he's maniacal and will do anything. Which is what makes him so dangerous. This series is just phenomenal too.
Dracula is one of my favourite novels, its absolutely incredible. I collect editions of this too! I've often felt Dracula, to an extent was merely lonely. He just wanted someone to spend eternity with...but when about it in the very wrong way! I think I'm due for a reread of this one soon.