Similarly to playing around with Ulm, you might try playing around with the
easy spell mod (Save this to c:\Program Files\Dominions3\mods directory or equivalent, and go to Preferences/Mods to turn on "All spells pre-researched"). Then you can select a nation like, say, EA C'tis and see how much you like their spellcasters. Realizing of course that in a real game you won't have access to all those spells from the start of the game, it might still be fun to see what magic schools you want most.
-Max