Use whatever meat you prefer. Traditionally, lamb is the most usual (I used beef in the photos), and you can even mix different kinds of meat.
If you can't find a ready-made mix of couscous spices, you can make your own from: cumin, coriander (ground), cinnamon, nutmeg, ginger, cardamom and turmeric. Paprika, cloves and caraway are also sometimes used.