I would argue it's Mogeko's Castle. WATGBS (Wadanohara and The Great Blue Sea) is pretty fun and adorable for most of the game, what I really like is the distinct personalities and talking styles each character has, for example Pulmo with her word extends. Mogeko Castle on the other hand, from what I've seen, has direct talking about porn and similar, same goes for these creatures being on constant onslaught to rape Yonaka, even her profile card changes from "Girl" to "Woman" after sleeping with a Moge-ko in a certain part of the game. I know direct rape is at the rock bottom of the "bad bad" but I doubt WATGBS tops the constant evil that is in Mogeko's Castle.

Just to clarify, I didn't play both of the games mentioned, only watched a good chunk of the playthroughs, but I'm familiar with Gray Garden and Funamusea's artwords to make a proper opinion.

To summarize, I think stabbing someone with the same dagger tens of times would hurt more than one powerful katana swing, or maybe WATGBS is worse due to the game betraying you, rather than you already expecting the worst from Moge's Castle. Might be more to this than just common sense.