It doesn't matter if your mozzarella is sliced or shredded (Giordano's, for example, used shredded). The best are Stella (used by Giordano's, although a commercial grade) and Sorrento, both of which have great flavor and mouth feel. I don't personallly like fresh mozzarella because I find it too bland, but that's an indivdual decision. You can certainly use any cheese you'd like!