X here=MG Fantasy (Of course!)
The book noticeably not on this list is Harry Potter and the Sorcerer's Stone. I LOVE that book, but have found that fervent "I never read MG fantasy" readers have indeed read that one MG fantasy book.
I also left off some other classically famous and popular MG to highlight books I feel demonstrate just how thoughtful and well-written MG genre fiction can be but don't get anywhere near the attention they actually deserve.
This was SO HARD to keep to 10. I originally had way more than that, but I take a sort of ruthless pride in keeping these lists at 10 and not going over.