Magic spring,ress,mass dragon slayer,mass magic schackles,trap,pain mirror,teleport,target,phantom,hypnosis,doom probably blind would be great but i have never found it o.O
gift is a nice spell but mostly for inqi so lvl 1 is enough , dragon arrows can be at lvl2 if you dont have 15+ int,sacrifice 2 is mostly enough, sheep is quite expensive spell .. those are good for every classes. For mage also some direct damages like fire rain,armageddon, also demon portal is nice

You can put it on friendly units if you want but of course that doesn't work for the strategy noted on the previous page.

A nice way to start against an army with at least 1x stack of non mind immunes is with Hypnosis + Magic Spring in turn 1. Now wait as the AI beats that unit stack to a pulp giving you all your mana back to cast...Kamikaze on the hypnotized stack in turn 2.

It leaves you with alot of opening options in turn 3 and alot of mana. you can detonate the bomb yourself by killing the weakened stack with your own units when Hypnosis wears off. Or the AI might kill it off and detonate the bomb that way but its great way to:

1) kill off a powerful enemy stack without having to do anything. And you get tonnes of rage for it too.
2) prevent most baddies from attacking or moving against your own units for at least 2 turns.
3) deal a metric tonne of damage to all melee units wailing on your puppet through retaliation and the spell Kamikaze.
4) leaves you with enough mana and rage + good unit positioning to cast whatever you want coming into turn 3 with little or no losses, even against armies much stronger than you.

It also sets up an awesome Pain Mirror because we are talking full enemy unit stacks attacking your puppet with total abandon.

Perhaps the topic should be:

What spells wouldn't you upgrade with a gun pointed at your head telling you to?

It's easy to find the really, really good spells that compliment your style of play. I tend to prefer the Phoenix as basically attack absorption for example. Yet, I'm still technically a "noob" and would like to know the spells not worth bothering with at all.

I'm a level 22 Paladin, and it's too late to realize that magic crystals aren't endless so that knowledge will help in my next gameplay.