I have so many favorite books in this genre, it's going to be hard to choose!
1. Caraval Series by Stephanie Garber
This series is set on a series of islands. It revolves around a game called Caraval that is led by the mysterious game master, Legend. It is almost like a circus, but players must be cautious not to get too swept away. Watch Scarlett and Tella uncover the game's secrets, go on wild adventures, and develop whirlwind romances. A super fun series for young adults. I would recommend ages 13 and up on this one for the romance side of things.
2. Ender's Game by Orson Scott Card
There are several books in this series, and although I've only read one, I feel completely fulfilled with the way that this book ended. It is such a fun adventure, and I enjoyed seeing Ender's progression from the start of the book to the end. The end is amazing and super unexpected. This is a set in space and perfect for any sci-fi lover! I would recommend this book for ages 14 and up. There are some heavy concepts and a few brutal fights.
3. Scythe by Neal Shusterman
This story takes place in a Utopian future, or so we think. The Thunderhead, an AI that rules the world, has fixed every modern issue we now have. People living in normal society have the ability to live as long as they'd like. With the ability to "turn the corner" and operate healing nanites for injuries, the citizens can live for hundreds of years. There's only one catch. Scythes roam society, gleaning citizens based on the statistics of age and how they might've died when the world was still imperfect. Most scythes are honorable and just with their gleanings. I said most. Follow Citra and Rowan as they uncover the secrets of scandals in the Scythedom, discover forbidden love blossoming within themselves, and learn the ways of the Scythe. A great read for young adults 13 and over, as there is violence, and concepts that may be difficult to grasp.
4. Cinder by Marissa Meyer
This one has been a favorite of mine for a few years now. A twisted fairy tale set in a New Beijing after WWIIII. Letumosis, a futuristic plague, runs wild throughout the world with no chance of finding a cure within sight. Cinder is a cyborg living with her stepmother and stepsisters in a small apartment. She provides for the family, while receiving ill-treatment herself. One day, while working her mechanics booth at the market, the prince himself brings her a droid to work on. And like that, the adventure begins! A great sci-fi and fantasy mix for young adults ages 13 and over. Be sure to read the next three books, as well as the bonus two.
5. The Hunger Games Series by Suzanne Collins
A total classic. The movies compare nothing to the greatness of the book series. The country of Panem is separated into 12 districts, each district manufacturing a product to send to the Capitol, the richest sector. Each district must send two children, a girl and a boy, to play to the death in the Hunger Games. The capitol claims it is keeping the peace between the districts, but really, it is for their entertainment and just a show of their power. Katniss, the main character, resides in District 12, in a poor area nicknamed the Seam. I won't spoil it, but Katniss unexpectedly gets sent to play. A brutal, bloody adventure, full of desperation and loss. This is truly a great book, and I praise Suzanne Collins for it. Recommended for ages 14 and up. It is bloody good characters die. I'll be honest, this series made me cry many times!