Which level of magic do you use the most (Heroes of Might and Magic III)?

I'm not saying he's bad. He's definitely powerful, but... I often find myself using speed or slow spells instead.
What do you think about such a "wonder" as the Mirror spell?

I don't like the Mirror spell; I prefer to clearly plan who and when to attack. Moreover, it's very difficult to guess what the opponent will use, and spending a magic turn to protect a single unit, especially when it's unclear from what, seems irrational to me. There are many other spells that provide a guaranteed result.