This is a tricky and complicated topic. We can offer some tips to make your decisions a little easier.
Selecting a text
Before you make a decision about books, you first need to have a clear idea of your coverage. That topic is discussed in detail here.
Casebook vs. home-grown materials
Putting together course materials for a two-, three-, or four-credit course can be a mammoth undertaking. The selection process can be quite time-consuming, and editing cases down to manageable size is not a small job. Before committing to such a task, you should see what is already available from law-book publishers.
Timing
Most bookstores want book orders two to three months before the beginning of the semester. If you place your order less than a month before classes begin, there is some risk that the books will not be on the shelves in time for the first class.
Obtaining review copies of casebooks
Law-book publishers are happy to provide teachers with free review copies of their casebooks. Your registrar or academic dean can put you in touch with the publishers' representatives who are assigned to your school. Many of the representatives are lawyers and most are quite knowledgeable about not only their product line but also the products of other publishers, as well. If you want to start the process yourself, you can contact the law-school division of the major law-book publishers through their web pages, e.g.:
Non-casebook materials
Some of casebook publishers listed above also have a line of student-oriented treatises and other study aids (e.g., hornbooks, nutshells, other types of course overviews). Be sure to ask for copies of these as well. It helps to know what the students are reading in addition to your assignments.
In addition to the publishers who have invested heavily in the law-school market, many other law publishers have products that may be useful as either principal or supplemental texts. AHLA, for example, publishes a popular Fundamentals of Health Law 4th edition text as well as many other titles that are more narrowly focused.