Traditional Chinese restaurants will serve san choy bau with beautiful crisp Iceberg lettuce leaves.  However, I rarely have the patience for carefully peeling off layers of Iceberg lettuce since they tear so easily.  So, for serving at home, although less authentic, I prefer using little gem lettuce instead.  It doesn’t have the same crispy texture but it is infinitely easier to peel off in perfect leaves, it is the perfect shape for holding in your hand neatly and it is a little more forgiving when trying to use it to wrap around a filling!  So, I often sacrifice authenticity for convenience in this respect.  Feel free to go for the authentic iceberg lettuce if you have more patience than me though!