The prefab sushi I can get is all California rolls (so avocado, which is good for you but calorically dense, and fake crab, which is low in protein and high in carbs compared to real fish), spicy rolls (mayo-based binder), and cucumber rolls (I don't like cucumber).
California Rolls, American Style Sushi Rolls, Sushi, How To Make Sushi Photo Tutorial has nutritional information for various rolls - figure 6 or 8 pieces to a roll.
I get the nigiri assortment when I can - just fish & rice.