Have 3 Lords, Raven, Oswin, Jaffar, Priscilla, Farina or Fiora, Dart, Pent and Rath for your units. In my play of HNM, they turned out to be the best ones. But really, if this was HHM, those units are some of the most needed, but since this is HNM, just pick ~your poison~ units that you feel will carry you until the final chapter with ease