1. Escape From Spiderhead
    In Tenth of December
  2. Civilwarland in Bad Decline
    In Civilwarland in Bad Decline
  3. Tenth of December
    In Tenth of December
  4. The Semplica-Girl Diaries
    I'm suggesting this be your favorite (which is odd) as I've been thinking about this list ever since you posted it and have concluded that while Escape From Spiderhead sticks with you emotionally, SGD is incredibly inventive in its rightful assumption that the reader - whomever is reading the diary of the author - is aware of this bizarre world. It forces the reader to solve puzzles and fill in gaps; Saunders transports you through time by letting you glimpse a diary of a peculiar future.
    Suggested by @Nicholas