Favorite book of your favorite series.
Hah, I actually already mentioned that! It’s Guards! Guards! by Terry Pratchett. The book is a marvelous fantasy, both using and mocking familiar tropes (the heroic orphan who turns out to be of noble birth, the stalwart good guy who won’t bend the rules even a bit, the villainous fellow who wears all black and has a small furry pet [usually a cat, but in Lord Vetinari’s case it’s a small, elderly dog], etc). This is the first of the Night Watch of Ankh-Morpork books and the first time we meet Sam Vimes, who starts out as an alcoholic loser and winds up repeatedly saving the city and rising to become one of its most prominent citizens over the course of a handful of books.
There is a secret society, dragons (both the big noble ones and cute little ones who ride on rich folks’ shoulders… and sometimes explode), mysterious goings-on, politicking, and heaps and heaps of awesome. I usually refer people to Guards! Guards! when they ask me which Discworld book to read first, that’s how awesome it is.