Mages – their development.

Personally, I always level up Luck, and when I also have artifacts that boost Luck to 5, it's incredibly effective...
Controlling machines - the Tent and Ballista work great....
Spellcasting - you can cast spells at an insane speed....
But with magic, you have to make some choices....it's all good.....

Chaos Magic...damage....
Light Magic - blessing your own warriors....and with spellcasting, you can bless your warriors in one turn so much that they become practically invincible......you can resurrect endlessly if you have a lot of mana....
Summoning Magic....I only use Phoenixes from it....
Dark Magic - It's a cool thing....you weaken the enemy so much that they fight like babies.....

I always choose Light Magic, and then whatever comes first...Darkness or Chaos....