Which school of magic do you prefer and why?

Water is also a decent school of magic, especially for Warriors – Clone combined with Phoenixes is a great combination. Prayer also provides acceleration, but it's an improved version that isn't interrupted by slowing effects, and Blessing and Mass Dispel are also beneficial for a Warrior.
However, you can't do without Earth magic. The other schools of magic should be chosen depending on the hero, the city, and the available spells and artifacts.