I'm using Frost Bomb, Incanters, and Crystal.
For trash, I just use orb on cooldown. If crystal is up I use it with orb.
For single target, it is a DPS increase to save orb for your crystal.
Make sure you're using blizzard on trash packs larger than 5 mobs to get your frost bomb back faster.
Note: Technically, for boss DPS images is the best. But throughout the whole dungeon, incanters simply beats the living fuck out of images.