Well, that depends on your preferences. 'Neuromancer' by William Gibson is often considered a classic in modern sci-fi for its pioneering cyberpunk elements and influence on the genre. Another notable one is 'Snow Crash' by Neal Stephenson, which offers a unique take on a dystopian future with virtual reality.
It's hard to say which is the absolute best, but 'The Three-Body Problem' by Liu Cixin is highly regarded for its innovative concepts and engaging plot.
There are many great modern science fiction books. 'Dune' by Frank Herbert is a masterpiece that combines politics, ecology, and adventure in a richly imagined universe. 'The Martian' by Andy Weir is also popular for its realistic portrayal of survival on Mars.