Audiobooks (Audible) — used for entertainment focused books and/or those books that I consider to be disposable.
eBooks (Kindle) — used for books that are shorter in length and/or I expect to read only once. (Note: if I find a hidden gem here I will often also purchase the physical book)
Physical Books — my preferred medium. Reserved for those books that I expect to re-read multiple times, are longer in length and/or I will need to make lots of notes/highlights in.