Which spells do folks consider worth learning or upgrading ?

[player1]

As mage with high intellect, it's obvious that I prefer damage spells from destruction school a lot, so I there is no need to much anything more about them.

Chaos school has also good debuff called Weakness, which is Mass spell when upgraded to 3rd level. Great in situations when enemy army is so big that damage spells would less reduce enemy attack potential then weakness itself.

From other schools, I always found Ressurection useful to keep loses to minimum if possible.

Magic Axe is useful too, early in game when you need to single out one target, and fire arrow is too weak.

Also Geyser is great spell if you can spare leveling Distortion school, since it will affect multiple targets (uo to 8 at 3rd level) without hitting any of your troops.