In terms of the fusing, it doesn’t matter if the fine silver wire is
dead soft or half-hard. It’ll fuse either way, and will become dead
soft in the process.
In terms of the winding the wire on a dowel to make the jump-rings
that will be fused, dead soft is easier because it’s less springy.
Personally, I’m really liking Argentium for L-in-L chains. It’s best
to use a slightly bigger dowel that Stark specifies, or a slightly
smaller wire gauge (it doesn’t stretch as much in the forming as fine
silver), but it’s MUCH easier to fuse and after the chain is made, it
can be hardened.
However, if you want to use it with PMC, it does have a
substantially lower melting point than fine silver.
Anyway: I’d recommend dead soft for either fine silver or Argentium
for LinL chains; that’s what i use, and it works well.