Weirdo, I have two questions for you that might help narrow-down (or expand) the units you should be looking for.
1) As the game expanded, parent factions and allied factions became a part of the game where it was acceptable to use the two together and be considered "pure" factions, as well as the rules allowing for movement & combat formations to be used between the allied factions. Do you want to go this route? It would add House Davion to the Swordsworn and The Republic to the Highlanders.
2) Are you interested in using mercenaries or gunslingers in your forces?
As for what to look for, that varies by faction, since each faction had its own flavor with benefits & weaknesses. The Highlanders often had higher defenses, armor, long weapon ranges, but low attack values. The Swordsworn I don't remember as well, but looking at stats they tend to have high damage, more special equipment. but run hot with average defenses. I can pull up my suggestions tomorrow when I have more time.