Storm Surge or Manablast for spell damage?

These items are very similar and I dont know which one would be better for spell damage.

 

I don't know which of these is better because I've never seen either used tbh, if you're looking for spell damage try like Nepta Floodbringer or Cascade. Unless there's a reason you want to specifically use one of these, in which case, not sure.

 

Your roll on manablast is pretty bad. If raw spell was really high I would go mana blast, but if you don't get a better roll go storm surge.

Even thought here are better wands, these ones are actually not that bad.