What book should I read?

The only books written at 12th grade reading level are nonfiction, usually related to law or a science, and specifically written for people in those fields to learn new things.

Good luck finding any fiction at a 12th grade reading level. You'll be lucky if you can find something at a 10th grade level.

Now, since those are the books you've chosen, then take the time to google each one to find out what grade level they're written in.

(Don't take To Kill a Mockingbird, since that's 6th grade level.)

I'd hesitate to read any Faulkner, he's inscrutable. Outsiders, Peace and Wicked seem a bit beneath AP English at the 12th grade level. I don't know anything about Fault, Uglies, or Truth. That leaves Gatsby. It's an easy read and theme and most of the characters are vile and despicable. So my question to you is why is Gatsby so venerated by readers and critics? If you want something off the list, try Night by Elie Weisel. A story that will shake you to your bones.

I'm a big Fitzgerald fan & prefer This Side of Paradise to the Great Gatsby.

You might try

Crime & Punishment

Ship Breaker by Paolo Bacigalupi

The Hotel on the Corner of Bitter & Sweet by Jamie Ford

A time To Kill by John Grisham

The Millenium Trilogy by Steig Larsson

The Great Gatsby. Don't pick popular books like The Fault in Our Stars as it is not considered a modern classic and more of a beach read. (I know it's a supremely good novel but teachers have a strict view)

The Great Gatsby. It's one of the titles suggested by the college board for the AP literature and composition exam open essay's. I'm not sure if this is a book of your taste but it is a great novel.

From your list, I would pick "The Outsiders".

Here are a few others:

"Ender's Game" and/or "Ender's Shadow" by Orson Scott Card.

"Dune" by Frank Herbert

"A Time to Kill" by John Grisham

"Without Remorse" by Tom Clancy

To Kill a Mockingbird, Harper Lee

The fault in our stars.

try

at first sight by nicholas sparks

it's the best book i ever read