Big heavy chain gives good caternary effect and prevents shock loading.
Moorings are usually designed at a 2:1 or 3:1 max scope, depending upon local regulations, so this means heavy chain is a must if you want any caternary and protection from shock loading.
Chain wears where the links meet. Anchors are not constant duty but moorings are. Moorings are exposed to wear & link degradation 24/7 365.
The biggest chain, or wire diameter, you can buy will last you the longest.
Galvanized chain adds no real long term benefit as the link wear chews through it rather quickly anyway so self colored chain is fine.
Long link mooing chain is a good option because shackle fit better through it.
You should have a top chain and a bottom chain. the top chain will be lighter than the bottom chain. A good rule of thumb is that the bottom or really heavy chain be 1.5 times max water depth. You will replace the top chain every three to four years depending on your location but bottom chain can last as long as 7-10 if big enough..
Depending on the bottom type you can use: Mud = Mushroom, pyramid or screw. Hard bottoms = Large diameter granite (low and flat is best). Cement is generally considered a bad idea, by just about every municipality that has studied mooring field failures, and many municipalities have banned it's use as it loses a significant amount of weight bellow water and there a re no real "standards". In this vein many have also baned "home made" moorings of engine blocks, cement filled barrels and such. Most require any home made mooring to first be inspected by the local harbor master.
Many municipalities only allow certain approved mooring companies to set, retrieve, inspect and maintain moorings. The anchorage I'm in now has over 1200 boats and they are very, very strict as to what you can and can not do!
Feel free to watch this video and you'll see the types of mooring conditions boats in Maine can deal with in the winter and during Nor' Easters. Most boats up here use the Wayne Hamilton mooring protocol as shown bellow. None of the boats in the video broke free despite a few of them having 15 footers breaking over them. One actually rolled about 80 degrees and popped back up but did not break free.
Please ignore my video skills..
Why Not to Cut Corners On Your Mooring System (LINK)
Photo Courtesy of Hamilton Marine (LINK)
This is my bottom chain for a 36 footer..
Bellow the ball pendant attachment causes the least amount of problems unless you have multiple floats and the "equator" of your mooring ball sits bellow the surface of the water. If the waist or "equator" of your ball floats above the surface of the water, no matter how many floats you have, it will wrap the ball and then get suck down to the chain as the boat pulls..