Tower-Construct Troops (Golems and Gargoyles), Genies, Nagas (Snake people) and Titans and mages, Gremlins as the workers/cannon fodder (second worst cannon fodder in the game, and valuable ranged units when trained)
Expensive (so slow buildup) and slow overland movement, but strong long range offense, the most spells (so more chances for good/game-breaking spells), and boosts to Hero spell capacity.
High Diplomacy and Research, low Martial and whatever stat is for mobility (at least until they can teleport/fly everywhere).
Locale: isolated, in terrain mostly unlivable without magic (tundra, desert, mountain peaks).
Listed as "good aligned" for Altar of Sacrifice purposes (only sacrifices artifacts).
Dungeon-Troglodytes, Beholders, Medusas, Harpies, Minotaurs, Manticores and Dragons
Third-most expensive and acquiring the red/black dragons is even more expensive, but secondbest ranged offense (harpies can be basically ranged attackers), black dragons are the strongest (city) unit in the game (plus magic immunity), and boosts to Hero experience.
High Intrigue, Martial, whatever is magic power instead of research, low Diplomacy (and low Stewardship?).
Locale: most isolated, in underground caverns and tunnels, contact with surface uncommon but very exciting.
Listed as "evil aligned" for AoS (only sacrifices creatures).
Inferno-Devils and Demons
Cheap, but you get what you pay for. Has a couple means of sacrificing cruddier creatures for better ones, and boosts power for Heroes.
High Martial, but medium otherwise, even Diplomacy. Somehow.
Locale: Neighboring three or four factions, in horrible lava landscape that they spread wherever they can.
Listed as "evil aligned" for AoS.
Necropolis-Undead(top end are Dragons, Vampires and Liches)
Middling costs, mostly mediocre troops, poor mobility, but glorious NECROMANCY, the means by which strength can be gained from conflicts, instead of slowly worn down. Good at outlasting things, strategically and in combat (vampire lords reason for only "mostly mediocre").
High Necromancy (everyone knows it) and High Stewardship, low low Diplomancy (undead give morale penalties to the living, in addition to penalties for trying to get too many factions to get along).
Locale: What used to be prosperous human lands, now huge dustbowl.
Listed as "evil aligned" for AoS.
Rampart-Centaurs, Dwarves, Elves, Pegasus with Elf Riders, Treants, Unicorns and Dragons
The frugal town; resource generation and decent troops for low costs (different dragons). Mostly very good mobility, with various forms of anti-magic (and still decent magic).
High Diplomacy, high Stewardship, low Martial.
Locale: Neighboring two or three factions, wants to be isolationist but can't help it; plenty of thick forests they get tetchy about.
Listed as "good aligned" for AoS.
Stronghold-Orcs, Goblins (some with wolves), Ogres, Cyclops, Rocs and Behemoths
Low cost, high offense in many flavors (including hero boost), slow troops (counteracted by mobility Heroes). Tied for fewest spells.
Best Martial, high mobility, low Research, low Intrigue.
Locale: Why the wizards aren't more isolationist; any badland will do, and they get around.
Listed as "neutral aligned" for Altar of Sacrifice (sacrifices artifacts or creatures).
Fortress- Gnolls, Lizardfolk, Giant Dragon Flies, Basiliks, Gorgons, Wyverns and Hydras
Medium cost, defense layered upon defense, good relative mobility in their own terrain (bad everywhere else), and lots of creatures terrifying in melee. Never really lost a war on their homeland, but sadly great defense cannot be used as offense. Tied for fewest spells.
High Intrigue, high Martial (defensive), low Stewardship, low Research, low Diplomacy.
Locale: Neighboring four factions, but rarely do the swamp-dwellers care.
Listed as "neutral aligned" for AoS.
Cove-Ocean Nymphs, Pirates, Flying Lizard thing, Humanoid Reptile and Sea Serpents
Other than great water mobility, I haven't the slightest idea; that's why I voted it.
Locale: Islands from which they can harass almost everyone.
Castle-Human Pikes, Swords, Archers, Knights, Monks, Griffins and Angels
Second-most expensive, with both a solid, well-rounded set of units and Archangels (which are the only serious non-Hero healers in the game, because once-per-battle resurrect), and boosts to mobility.
Highest Diplomacy, high Stewardship, low Intrigue.
Locale: Neighboring almost everyone. Often get wars on multiple fronts, despite Diplomacy.
Listed as "good aligned" for AoS.