What kind of spell do you like?

well, here again, it depends on who you're playing as and against – everything depends on the goal of the battle. I can name spells from each category that are my favorites. But if you're playing with an army, as is often the case, the priority is probably as follows:
1. Blessings (I really like them)
2. Curses (but not death curses, but order curses)
3. Summoning
4. Combat
5. Travel