I haven't played around with the schools of magic too much and I was wondering what you think the best ones are. Since it may be hard to narrow it down to just 1, list your top 3. It'd be interesting to see what you think are the worst schools of magic as well.
I define the school of magic to be useful if it has spells that can do some or all of these 4 things: damage, utility, protections, and buffing/cursing. There are other more subtle benefits to certain spells (like being able to interrupt casters with Magic Missile), but to make things simpler try to stick to these categories when deciding which schools are the most useful:
Damage is just anything that's pure damage such as: Magic Missile, Fireball, Skull Trap.
Utility is some sort of usefulness outside of just combat. Many skills are both utility and buff/curse. Charm,Invisibility, and Friends are utility, although Charm and Invisibility can also be used in battle.
Buffs/Curses are any type of magic that changes an ally or enemy like Luck, Haste, Charm, or Ray of Enfeeblement. I excluded Shields/Protections from Buffs because they are such a huge category.
Protections and shields are any type of spell or damage protection, including level 1 Armor, Ghost Armor, or Protection from Stone Turning (forget what it's called).