If you don't know what these villains are from here's a answer

Nowhere King: centaurworld

The Lich: Adventure Time

Bill Cipher: Gravity falls

Anti-pops: regular show

Everybody here apart from Nowhere King, as I am yet to watch his show

Hmm. I'd say it's either Bill Cipher or the Lich. I suppose this comes down to if you want a entertainingly evil villain or a terrifying villain. Don't get me wrong, Bill is scary, but he's also funny and more deliciously evil, whereas The Lich is just outright scary and has almost no funny moments, which is the point of his character. Personally, I prefer The Lich since I love a scary villain in a lighthearted show, but I could also definitely see preferring Bill.

Blitzo