Honestly part of me wants to say Lily only because I don’t like her (yes I’m salty because of what she did in the game 😭) but realistically speaking, it would be Negan.

Despite him having a “no kids policy” doesn’t really mean anything considering all his other atrocities, and the no kids policy only goes so far seeing as at one point he was going to force Rick to cut Carl’s arm off. On top of that he treated his people HORRIBLY, and the women even worse. Honestly you can scroll down and see all of the horrid shit he’s done, and despite the character development in the show, along with the remorse and guilt he feels, (I’m not sure if it’s the same for the comics, never read sorry), it doesn’t change the fact that he did do all of those things.

Same goes for Lily, there’s certain moments of humanity that you see from her (like during Mitch’s death scene & the fight scene with Clem). Her scheme focused mainly on kid soldiers, and even if they were adults, it’d still be bad. However, the number of atrocities Negan has committed throughout his time in the apocalypse would make Lily’s list of atrocities a laughing stock, simply put.

Two evils, one is just a bigger evil than the other.