Short is better than long. While long articles can give you all the details of an idea, it may be better to read lots of short articles from different researchers than a few long ones. In this way, you can quickly get a better feel for the breadth of a field. With respect to refereed publications, books are an interesting case. Books may take longer to get into print than journal, conference, or workshop articles.
Books are longer than articles.
An author has to discipline themselves very strictly in order not to over-fill an article. However, a book can be any length and may be full of padding. We have said above that web pages are not refereed, and therefore are not good sources for reading. Further, there may be enough information on a web page for you to decide if you really want to read more by a particular author. Note that web pages have another problem.