Originally Posted by woodscrew
So, I never thought about this until I read an article somewhere a couple of years ago. It doesn't make much difference either way. Unless your anchor is stuck somehow ( in a rock/coral crevice, buried way deep in hard bottom) and will not pivot around with a wind shift or tide change. With the shackle pinned to the anchor the chain will be side loading the shackle and potentially bending it. Whereas if the shackle is pinned to the chain the bow part of the shackle can slide around in the shank, no unfair loading on the shackle. Then you only have to worry about bending your anchor.
If the shackle is held pretty straight in either the anchor or the chain link...according to rigging best practices that I have read it shouldn't matter.
However a long pin in either chain link or anchor shank and the shackle can twist and be compromised..pick your poison.
Without adding anything...whichever way the shackle can twist the least is the best way.