Author Challenge, Day 9: Favorite Book by Another Author

This is actually a very difficult question!  There are so many authors that I admire.  A series of novels that have recently stuck with me and someone who’s writing style I very much admire is Sarah Maas.  Of her novels, I think my current favorite is Heir of Fire, but I reserve judgment as she has more books coming out this year.  I particularly enjoy Ms. Maas’s complex characters and outstanding world building.  

What’s your favorite book?