Only one novel per person! Any genre, tags, the only requirement is that it must be your favorite novel of all time. To start it off, my favorite is probably Reverend Insanity.
Oh, my dear friend, what you're asking is really hard because I'm thinking of a lot of novels rn lmao. Still, if you only count the completed ones, I guess my favourite amongst those I have read would be Release that Man. Not sure if a lot of people know this but it's a hidden gem poorly rated by people complaining it has no romance when the novel typically has no romance tag.
Where the Red Fern Grows - An absolutely beautiful story about a boy who is mad for dogs and his two dogs. A brilliant novel - It will make you yearn for dogs as he did, root for him as he goes around working his ass off to earn enough to buy two pups, and cry big fat tears with his every success and failure
I remember that they made us read this in primary school and by the end of the novel everyone in the class was bawling. Stuck with me to this day as a reason I don't want dogs, it would be too damn sad. Anyway, my personal favorite is Way of Kings by Brandon Sanderson.
Reborn as My Love Rival’s Wife Its my favorite in 3 genres: Romance, Gender Bender, Comedy. Its the best gender bender romance I've read, and it's also the funniest novel I've read on this site.
I'd say Daoist Gu as well but since it's already mentioned I'll say Transcendental Mechanic (aka The Legendary Mechanic)
NEET Receives a Dating Sim Game Leveling System my favorite genre : action, romance, harem, school life, fantasy.. other than its excessive emphasize on MC's handsomeness, it still left quite a huge impression to me as it managed to have a good balance on romance-harem and school life-fantasy..