Hard cover or paperback, which is your option, there are arguments to support both types of books, and many will come out in both forms, at some point. If you are self publishing, the option of whether or not to offer your book as a hard back cover is up to you, dependent on your personal budget and your goals for the book. Traditionally, books will enter the marketplace as a hard back book. Then, over a few months or even a year later, the introduction of the paperback book to the marketplace, offering a potential for another round marketing and promotion to sell it.
For those planning to self publish, publishers allow for the author to gauge the need to use hard back books on their own. As can be imagined, the hard back book does cost more to produce and therefore the cost of having your book produced in a hard back fashion can be much more expensive. For those who will use print on demand, the costs may be lower as it allows for the buyer of the book to determine if they want the more expensive hardback book or the paperback book to purchase. Some of those higher costs are helping to defray the costs of production of the hardback book for the author as well.
In situations where you will work with your publisher to get the book out in print, the publisher may go through a process of determining if the hardback book is a good investment. For example, some financial books, how to books and other instructional books do better when they are released only as paperback books. They are more of a workbook, then, and give the reader the ability to use them as such.
The publisher may also decide that there is a need for a hard back cover, though. For example, in fiction works, there is a strong draw to the hardback book over the paperback. In particular, hardback books do well if they receive heavy marketing, and they are by well-known authors. Still, the publisher may decide that there is enough interest and less risk and therefore the investment into hardback books is the choice.
Ultimately, most of the publishers today, including the larger publishing companies, are holding off on investing in hardback covers for most unknown authors and first time publication choices. They are finding the investment to be too much of a risk in the current book buying trends. Rather, once an author begins to do well, they may consider hard back investments. The problem here is that book retailers are shipping back many of the hardback books they have received unsold.
Paperback is often the best place to start in the production of a book, especially for those who are first time authors. The lower costs allow for the better return on profit will be available, and ultimately, if there is enough demand, the publisher can go back and construct the hard cover books later.