certian factions have unique hireable units that are unable to be compared to anything else, take the wood elven scout and the gondorian tower guards, i think that all factions should have a unique unit or two that is based off the lore and fighting style of the faction, can do something nobody else can and truely be a unique force to be reckoned with.
name, dol guldur assasian.
faction, dol guldur.
whats so unique about it? it strikes from the shadows, able to execute a quick dash attack with its poision dagger and fall back for another strike just as quickly, it has low armor but can cause chaos on the battlefield as it rapidly moves in and out to strike.
name, dwarf defender.
faction, durins folk.
whats so unique about it? the dwarf defender is the frontline, he is the shieldwall, he is the tank. clad in full dwarven armor, he has twice the HP of a normal dwarf and has the unique ability to taunt nearby enemy NPCs to attack him (forcing nearby enemy NPCs to change there target to him), when fighting a player he is still quite hard to kill as his HP and armor keep him in the fight far longer then most soldiers.
so, those are two examples for unique faction units (and if you are asking, the dwarf axe thrower is shared by two factions, these unique units are for one faction and one faction only.) have a happy new year in middle earth!