Amnesia: The Dark Descent or Penumbra: The Black Plague?

[Googolplex]

Penumbra is better than Amnesia, but especially Overture, not Black Plague.
The reason is that there is less massive note reading to tell the story, there are much more challenging physics based puzzles, and the game felt not like a "game". Horror in Penumbra wasn't forced (like screen effects etc.) it still felt earnestly. The dogs, spiders and the infected were scarier than the grunts. Penumbra has the option to examine objects and read the player thoughts, the diary notes also are better formulated which takes a big effect to the immersion. And in the mining complex/shelter I felt more "isolated" and in danger than in the castle.

Overall Penumbra is a better experience with much more content and complexity than Amnesia.

But when you ask only about Black Plague and Amnesia, I think Amnesia is a better whole game, because the end of Black Plague is a bit strange and the game is too short.

Also scarier means not better, and I think that Penumbra is at least as good as Amnesia. And when you compare the Collection to Amnesia, Penumbra is even better.