Paperback books are made to be cheap. They usually have a thin card-like or paper covering. These covers are inexpensive, but they are more prone to bending, tearing, and becoming mangled with time. Hardcover books are built to be more durable. Their covers are resistant to being bent or torn. They also usually come with a dust cover or a dust jacket to protect the book from wear and tear. Hardcover books, as a result, tend to be more expensive.
If you want a book that you are probably going to read again and use as a reference or want to keep around possibly for others to read such as children, friends, or students, a hardcover is a good choice even though it is expensive.
For a book that you are probably only going to read once and don’t care if it gets passed on, a paperback book would probably be most ideal since it is less expensive.