I have read a few S-Tier fantasy books but never came across an S-Tier science fiction book.

I start to believe there's no such thing as an S-Tier book in that genre.

Used to build @kiwi | https://macbudkowski.com/

Some contemporary ones I haven't seen mentioned: 

If you like action-y hard scifi, The Martian is good.

If you prefer post-apocalyptic, there's the Wool Omnibus, Station Eleven.

I loved The Expanse books (especially the 2nd onward), even better than the show.

All of Ted Chiang's stuff is excellent.

A doodler and computerer. I like permissive/permissionless open source, smart contracts, p2p systems, room-scale VR, and NixOS.

shazow.net

Currently: WhatsABI

+1 for The Martian

Project Hail Mary is even better imo