These type of questions don't take into context, which is critical to this discussion. Are you taking on the trollfens? Than you better have fire. Are you taking on the Ark? Shock is your friend. Etc.
And elemental damage is only part of the total damage equation. It's possible to have a higher damage output even if the elemental damage is less, or negated.
So there's no real answer.
As a general go-to weapon, Spirit might serve you better overall simply due to the versatility of the elemental type. However, if you do the following standards you get the following results:
1) Fire element is the only one needed to complete all quests. You need to kill trolls in the arena to complete that quest so even running from trolls won't stop you. Taking on the Arc with a poison dagger might not be smart, but it's doable.
2) If you keep track of extra damage on an average, straightforward playthrough, , shock does more damage and more extra damage than any other element. That's mostly because ghosts and Ark enemies are weak against it. There are several enemies immune to shock so see the context matters disclaimer above.
3) Almost nothing is healed by poison (save those poison elementals) and lots of things are weak against it. So poison helps you, and practically never hurts you.
Context matters so really this discussion is not useful for general weapon choices.