Right now I got the 3* versions of both guns and I'm trying to find a gun I can use to destroy turrets.
I would get a Nova Driver but I already have a Silversix and I don't have any guns that can cause status effects so I'm considering upgrading the Voltech Alchemer first.
Now which one of these is more useful against turrets or as a general use gun?
Nova Driver vs Storm Driver
For turret bashing? You'll want damage, since shock is not the most reliable for interrupting turrets. It may shock before they attack, or after, but likely not during their attacks. As some have said, killing is the best form of cc. Something to consider, the polaris line. Interrupts with expanded shots, shocks, and destroys turrets like no others. However, it is not for general pewpew.
Between nova and storm, nova would probably be better for both turret and general use. Silversix, and by extension argent, are already good for turret killing, since they have an edge in single target dps compared to nova.
The reasons you would get another elemental gun once you already have an ap/alchemer, is for playstyle and preference. I don't know your playstyle, I don't know if you are a gunner, or want a sidearm, or your definition of "general use." The main difference between antigua and alchemer, is the mechanic. Single target, or ricochet type. Alchemers could beat antigua in single target, but one has to be skilled with the ricochets to be able to do so. Conversely, if you are facing a large mob, an alchemer will be able to do more damage to the mob as a whole.
As Demonicsothe said, polaris line is the best gun against turrets. However, it is not popular for party play since many people do not know how to use it without pissing off other people. (Polaris - Not good for parties, great for soloists)
Now, polaris is the best, but alchemers follow it very closely. If you can use the ricochet properly, you can do massive damage to turrets quickly. Also, if you use the charge attack w/ ricochet, you can 1 hit KO a gunpuppy (not sure about polyps, but still possible i think).
So: Nova vs Storm? I suggest Storm: You already have silversix for pure elemental, and while nova does more damage, storm's shock status is also very useful in the rest of the clockworks. On turrets, you can still kill them very fast with storm (i use one, and as said before, charge attack can 1 hit them). So keep the silversix -> argent peace for pure elemental damage, and get the storm driver for good elemental damage + a status.
Nova will always do more damage. Its good for that.
Storm can status and interupt enemies and deal some shock damage. Its good for that.
If you want, friend me and I'll demo them for you... but tell me something like "I'm friending you so you can demo these" if you do.
IGN Fehzor