For me, choice of preferred suppliers comes down to cost and convenience. With particular reference to physical resources, I believe that having a few solid suppliers is ideal. For me, whilst I would prefer it to be the cheapest (so my budget will stretch further), it more so has to be price competitive. Because my time and effort is money also… If I personally am wasting hours on fine-tooth comb-checking which book is a dollar or two less between multiple suppliers, I am using my own time less productively (which would be far better spent on other library initiatives).
My preference will always lie with having the physically ability flick through a book in making a decision as to whether or not to purchase. However, in this day and age, it has become less of a possibility to do so. Teacher librarians are generally more reliant on online selection aids, such as review sites/blogs for example. However, these resources and text suggestions must be evaluated with a critical eye to determine suitability for one’s own school community of learners.