Matrix Switchers are something you usually know about if you need them, so we won't bore you with possible reasons why you might need them.
The main choices involve the types of Audio and Video you need to have matrix switching for, and the number of inputs and outputs you need or may need in the future.
Quality also is a consideration, when quality is of paramount importance, it is not usually suitable to go with the least expensive switch. Check out the specifications and features of high end manufacturers like Key Digital when you need the cleanest possible signals.