Here's the thing: you are about to do a solo vanaduke run. You won't bring black kat set nor chaos set, no swiftstrike buckler and no blitz gun (not even the poison one), also no seraphynx sprite.
What will your loadout be? Also, what will your strategy be during the boss fight with the loadout you picked?
You can kill Vanaduke without guns, especially if you water the orbs. But Vanaduke is dramatically easier with a gun.
Just about any non-shadow gun will work. I've soloed Vanaduke with Valiance, Blitz Needle, old Callahan, new Callahan, Argent Peacemaker, Nova Driver, Storm Driver, Hail Driver, Polaris. And I'm not an especially skilled gunner. And much of this was before Black Kat and buffed Chaos.
So, to answer your question: Just about any non-shadow gun and some gunner armor such as Perfect Mask of Seerus or Shadowsun.