While it's really up to you, I'd recommend that you just make your cables with some quality Canare or Belden coax. The small amount of conductivity you gain when using silver is so small that it's pointless to spend the extra money. Also, silver isn't a fan of being flexed, so the conductor is more likely to break.
I could drone on and on, but you're better off making your own cables with some quality coax like Canare LV-77S or Belden 1505F.