Generally it's better to take shields if you plan on using smaller blocks of Vulkite, and double weapons if you're running a large block. Since the save after save is so much better in big blocks you lose value on the shield saves. If you are running shields, axes or picks is a hard choice. I guess that would depend on how much death you see playing against since the new nighthaunt can ignore rend for the most part. But someone ran the math and picks become the best when attacking things with a good save (like 3+) and you give them the runesmiter buff.
The shields Mortal wounds on charge did get a slight nerf that reinforces this aspect, since now you can only throw a shield on a charge if the model is within 8" of the unit you are throwing them at. Before you could charge and throw all 30 regardless of distance.
So ymmv.