In this game, speed really rocks. For example bringing your speed from 6 to 18 (savant gear – wizard T3) means you actually get 3 times as many turns. Any gear that increases your speed in this game is great, and you should go for the speed-oriented sets as much as possible. Speed is much better than power (attack) for DPS.
But you should also keep in mind that your tank (the guy you put at the front) should have very high defense and HP or he’ll die in 2 sec. This is why knights are great even though they have very low speed.