Virtually all guides I've read favor FIRE for the added damage.
I would go with
fire selecting the imbue, fire shield, flame body, fire protection, flame wave, and the passive series. I would add the
lightning grasswalk and passive. Max the Heuksal Soul Departs spear, Ghost spear, Chain spear, Flying Dragon spear, and passive. The above combination should work pretty well for PvP and PvM, and not require too many skill points.
Personally, I added a little into the Cold and Force passives to get the added defense and MP. Most folks think that's not a good idea because it uses valuable level points with little benefit, but it works well for me.
Also, I have been tempted to carry a bow as a second weapon and utilize a few of the bowman skills along with the passive. I saw a guide once that made the combo look very attractive.
Hope this helps,
twarg1
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