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I agree that stopping time is the most powerful spell in the 6th installment. It provides control and also allows you to damage the controlled unit. Meditation is also a very useful spell, offering excellent mana regeneration; I use it towards the end of the battle (when I have 150+ mana, it regenerates very well).
I didn't find mass draining very useful, but I actively use mass restoration.
Regarding elementals, I really liked the air elementals (which look like glows, not the ones that deal damage with lightning). They have an ability that deals damage and blinds the opponent for 2 turns. Awesome! :)