Ebook for fiction books. The convenience is amazing and i don’t have enough space for all the books as physical copies in my place. Plus generally much cheaper to buy.
I do however buy some non-fiction books (ex. books on writing/editing/crafting techniques/etc.) as physical copies as I reference them more often and searching is much easier in physical format.
It really doesn’t help that over the last few years I’ve been getting all sorts of ebooks on sale thinking I’ll get to them eventually, they’re on sale so it’s not so bad, it’s fine… hundreds of books later.