Best single target lightning spell

[Morendie91]

As title suggests, I'm lvl 72 and primarily use arc and sometimes divine ire, I nuke mobs instantly, but soon as I hit lot of rares the damage falls down to almost nothing. Bosses can be harder but lets me real, rares have the tendency to be stronger then map bosses with there random buffs. I cant figure out a strong single target lightning spell specifically for fighting those 1v1s, I usually end up trying to avoid or run away from the rares and nuke the other mobs, the rares slow my damage down so much they end up killing me.