Here we have two options of guns specifically for FSC zombies and Vana himself: a normal Hail Driver and Blitz Needle with a UV of Dmg Bonus vs Undead Medium. In terms of playing style, I am okay with both guns, so I want the gun with a better dmg output. I don't know how big the different the UV would make, and does it make my Blitz Needle better.
P.S.: Argent Peacekeeper is out of the question since I really don't like the Antigua line.
I would personally stick with the Hail Driver to have crowd control over the zombies. If you can clean them up fine enough with the Blitz Needle, though, you should go with that to put the hurt on Vanaduke.