These are my favorite units:
Griffin: Excellent damage-dealers because of the unlimited retaliation ability. Just get them in front of the enemy and keep pumping resurrect while your archers shoot the living crap out of the enemy.
Emerald Green Dragon: Both talents are excellent for utility. The area attack spell can easily regenerate 25-30 mana every 3 turns while doing 50-70 damage to every enemy around the dragon. The other talent is also great, you can first make your dragon wait, then at the end of the turn you can make him drag an opponent one square so he's next to his buddies, then use the area attack.
Elven archers (both of them): Simply great damage. not against bone-creatures tho
Inquisitor: I use these to punish the undead, also as far as I know inquisitors have the only spell capable of resurrecting lvl 5 monsters. The other talent which blesses a target and makes it do 50% extra vs undead is also pretty good because of the fact you also get some rage.
Cannoneer: Salvo owns.