Great game. I always combine Life and Chaos magic. Archangels with Eldritch Weapon? Torin with every Chaos/Life buff?
High Men Paladins are powerful against fantastics and spellcasters, but can actually be beaten by archers/pikemen(who cancel their charge ability).
Dark Elf Walocks, on the other hand are deadly(except against Paladins). Unlike normal Magicians who can cast Fireball(damage = 5xfigures in target unit), they cast Doom Bolt(instant 10 damage, blocked on by Magic Immunity), independant of the main ranged attack.
A quick overview of each magic type:
Arcane: Basic utility spells, also has Spell of Mastery, which wins the game instantly.
Life: Healing spells, obviously, but various buffs, as well as total control of planeshifting. Cannot be taken and no spell books will be found for Death if you already have Life.
Death: Sabotage spells, plus a combination of cheap and powerful summons. Life spellbooks cannot be taken or found if you have Death.
Chaos: Direct attacks, offensive buffs. Also some nice city attack spells.
Nature: Defensive buffs, reconnaisance, and even a spell that alters mineral deposits.
Sorcery: Time control, summons, illusions, and spells tha control enemy spells.