This is purely racial bonuses
TROG They have Juggernauts which are excellent troops, among the most powerful in the game. they have 80ish HP, do triple weapon damage, do splash damage to those that surround the one they attack, and do maul, so they continue to attack until they kill what they are fighting or miss. Trogs also have the ability to berserk and they get a +20 weight capacity.
MEN has Henchmen, in players hands, probably at least if not more OP than Juggs. In the AI, not so much, they don't seem to make good use of them. Also has +10% exp bonus for race.
IRONEERS have Golems. Great Damage takers, but certainly not the game changers that a Jug can be or as versatile or potential as henchmen. Their damage dealing is too low. Race also gets +1 hp per level, 30 spell resistance but tactical spell penalty.
QUENAR Have slaves. Slaves have no upkeep cost and are quick to produce, their strength lies in their numbers and speed at which they can be cranked out, very useful for both player and AI. Race also gets 50% fire resistance but -50% cold resistance. Fire resistance is more than worth the cold penalty, as fire is far more common an attack than cold.
The rest have no special units.
KRAX Krax gain the ability to fortify tiles, making them difficult to hurt along with a +10 bonus to their defense when under 50% hp. This is a little wonky with trained units, as the +10 doesn't seem to work when the entire unit is less than 50% hp, but when the last member of the unit is less than 50%, so that means almost dead. I might be wrong on that, need to look into it further. But anyways, the fortify is a great ability.
TARTH They get a +3 to attack and initiative if their armies are in groups of 3 or less. I have really mixed feeling about this one, pretty useful in early game, worthless in meaningful battles later. Helpful if you use powerful champs with minimal support and excellent in early game
AMARIAN Get bonuses from the number of shards their nation has, and a -1 hp per level penalty. This is pretty awful actually, you gain nothing early game, and just have a penalty and if you survive long enough to have a few shards, it's rarely very meaningful bonus, with the exception of the initiative bonus is which is at least something. Pretty terrible overall.
WRAITH These heal when they kill their enemy. 3 hp a kill. Now, it's a total of 3 hp, so a unit of 7 that kills a unit doesn't get 21 hp, they get three. This can be of some bonus for champs and your sov especially early in the game, but quickly becomes irrelevant and not nearly as good as their -1hp per level is bad. Pretty awful too. Also have a special trait they can add to troops that grant 3 mana a kill, pretty worthless.
MANCER They get +1 accuracy per level, and have a trait to add to trained unit that allows them to build roads, I like it.
URXEN They get a +2 attack when they are in armies bigger than 5. This is a pretty good bonus, it's not great, but useful as 5 man armies open pretty early in the game.