A couple of weeks ago, whilst laying up our Mystery in the Corfu Boatyard, I saw that the guy next to me had lowered his ground tackle onto a piece of ply. Being a nosy so and so I wandered over and took note of his method of connecting his anchor to the chain! Stainless shackle from the anchor to a stainless swivel, stainless shackle to the chain.
In Alex & Daria's excellent book 'Happy Hooking The Art of Anchoring' they do not recommend the use of swivels and I quote "We do not recommend the use of swivels on an anchor rode. Under normal circumstances you do not need it. Whether you have a chain or rope rode, it should untwist all by itself when you weigh anchor obviating the need for a swivel. Perhaps the only circumstance where you might consider adding a swivel would be if you were to anchor your boat for a very long period of time. Then, just as in a permanent mooring setup, you should incorporate a heavy duty swivel, as your boat is liable to swing around many times."