Dune. Definitely Dune. The most epic sci-fi world that is so far in the future it feels like it could be middle earth. Politics, mysticism, prescience, intergalactic travel build an amazing world that feels utterly alien but still relatable.

It’s like reading about modern battles between oil, culture and money, but in countless years and star system into the future.

Honorable mentions for Hyperion and Neuromancer for my favorites :)