Faction balance + quick guide.
chaos - great, summon fire elemental, hell hounds - magical aoe dmg -> fireball spamming, 1st place.
astral - op throught astral gateway, mana beast tanky enought to take cities, summon air elemental - spammable and counters melee units, 2nd place.
nature - trolls + stone throwers - okayish for sieging, insects summon can counter undead & astral (no aoe dmg), poison dmg takes forever to kill somethign from aoe cast and useless vs undead and astral summons, 3rd place.
death - no aoe dmg at all, 0 mana upkeep non-regening zombies/sceletons as scouts, overall - not that good, at least fear as aoe, but annoingly you have to finish feared armies 2-3 times (and preferrably without caster, or those enemies can run forever), 4th place.
holy - took me forever to win on impossible, paladins + battle healers can rampage through t2-t3 units, but countered by chaos/astral, nature with insects is annoing too kill (no aoe, except angel/archangel). Archangels - okayish for regen, meh for dmg & sieging, last place.
Most useless research tree - enchantment (except for death). Conj - good to great, evocation - ocasionally usefull.