The Illuminae Files trilogy is so good!
Current favorite sci-fi series would have to be Illuminae
The Martian by Andy Weir. Funniest book Iāve ever read
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A Wrinkle in Time by Madeleine LāEngle
The original Dune series!
The Skyward series by Brandon Sanderson!
My favorite Sci-Fi series has to be the Lunar Chronicles.
Legend Series by Marie Lu
I love the Remembrance of Earthās Past series by Liu Cixin.
I loved Artemis fowl books!
The Earthseed series
I really like Enders Game - Orson Scott Card
Iām realizing I donāt have enough SciFi on my āreadā list - a lot on my TBR pile thoughā¦ I want to read The Lunar Chronicles soon, it sounds like itāll be right up my alley, and by the amount of times itās being listed here, Iād say it must be good!
If we consider dystopian novels part of the SF genre then The Hunger Games, Divergent, and Legend (Marie Lu) series are all on my favorites list
I love the Illuminae series, Ready Player One, Otherworld series, and though itās not a series, I loved The Martian!
The Lunar Chronicles! Theyāre such great books!
Any Ray Bradbury, Brave New World, Red Rising, The Handmaidās Tale, A Wrinkle in Time, War of the Worldsā¦ There are so many great ones to choose from! 
My favorite Sci-Fi series would be the Red Rising Saga. All of the books were so captivating, action packed, and easy to read.
The Wayfarers series by Becky Chambers and really any Bradbury!
Currently it is the Murderbot Stories by Martha Wells. So fun!
I loved the Broken Earth Trilogy by NK Jemisin!