prime79
I usually choose Naadir because of his specialization and starting skills. The specialization allows you to summon ghosts onto the battlefield from defeated enemy units, up to the size of the killed unit, but not exceeding the hero's level. That is, if we have a level 5 hero, then by killing a unit of more than 5 creatures, we will get a unit of 5 creatures. In battle, this help significantly affects the outcome of the battle, because you can cover allies, take off retaliatory attacks (taking into account the incorporeality of the ghosts, this is very convenient), and just interfere with enemy archers by killing a unit near them. And if you also have a well-developed hero, then the ghosts will be even more useful.
Development
By choosing Naadir, we get everything we need at the start, namely: "Summoning Magic" and "Dark Magic". They are needed to go for "Horror" ("Banshee's Cry" additionally reduces the enemy's morale by -6). I usually start developing with "Necromancy" and all the skills there, because some affect the skills in other abilities, and there is everything you need: "Spiritual Bond" allows you to restore mana from enemies, "Banshee's Cry" reduces the morale, luck, and initiative of the enemy, and "Eternal Slavery" allows you to raise some of the creatures lost in battle, for example, two or three vampires or dragons. "Necromancy" itself allows you to raise more creatures, which significantly increases the army at the start. Next, I develop "Summoning Magic", in it I take "Master of Life" so that the "Raise Dead" spell works better, and then you can go around the skill wheel to "Horror" and take "Master of Spells" (+4 spells for the "Summon Elemental" and "Summon Phoenix" spells) and then "Banish" (Deals damage to all summoned enemies depending on your hero's level and the level of "Summoning", most effective when fighting demons). Then I start developing "Dark Magic", where I take "Master of Curses" (the "Weakness" and "Feeblemind" spells affect all enemies) and "Master of Pain" (the "Plague" and "Disrupting Ray" spells act in a 4*4 area, convenient against "boxes" covering archers). Next, you can take "Dark Replenishment" (returns all spent mana if the Dark spell does not work), but if you are not going for a super skill, then you can take "Master of Mind" (the "Confusion" and "Slow" spells affect all enemies).