The Hitchhikers trilogy. All 5 books of it. Every interpretation adds a little something to the mix.

Someone else said all of Pratchett, and I'll agree. My Discworld end goal is to own the physical, digital and audio book for each discworld novel.

I'll also add in the Bobiverse books, and project hail mary. While both are excellent in their own right, the audiobooks are really something special.