The Best Silver You Can Stack?

MY opinion:
The best silver to stack is that for which you will pay the lowest premium over the pure silver price.

If you are a silver stacker your primary interest is the price of silver, not the added numismatic value otherwise you have some degree of numismatic motivation.
Nothing wrong with that.

From a purely silver stacker point of view the order of preference should be:
1. pure silver bars in the largest sizes possible, so that the premium per ounce over the silver is as low as possible
2. silver bullion coins - but not proofs, in lowest grade possible.
3. 90% silver coins, taken at face value, from CRH'ing activites (Why 3rd place? - because refining costs have to be paid.)
4. other bullion coins against which some premium has been paid, such as proof bullion coins.
5. World scrap silver coins. (That is the area in which I accumulate, because they usually come as "by" purchases that have been included in larger numismatic job lots)

I'm partial to 100 oz bars: very low premium, nice size, easy to sell and not worry about shipping.

The best silver to stack? Silver that's free, from dirtfishing or found at face via roll hunting. I've gained thousands of silvers that way. If I can do it, so can you.

Philosophically, the scrap silver that I have accumulated over the years, has all come as a zero cost in numismatic job lots, relative to the targeted numismatic item that I was interested in that job lot.

The actual cost of the scrap silver that I have accumulated can only be guessed at.

Best silver is the largest bullion bar you can afford. The best bullion bar is the one without pretty pictures that you don't get attached to. The best bullion bars are square or rectangular so that they take up all of the room in your safe or hide-y hole. The bar should say what the product is, what the purity is, and how much it weighs. If your silver does not tell you what purity it is or what the weight is, then the next guy buying it will scrutinize it and maybe pass on it. That's not liquid. Sugar water isn't water.

I say this because I see bullion in the shape of skulls and whatnot, and I just feel that that style of stacking is for kids who are gripped by images and flashy stuff. Be smart. Pay the least amount possible. Purity should be .9999, otherwise you have to smelt the coin to get your actual silver. US coins are dumb because they rely on a face value for worth, and they never weigh the same from coin to coin, regardless of how many silverbugs can recognize silver (most people can't and are not aware that silver coins once circulated). Honestly, you'll be spending those coins at face value because most people just don't care enough to know what silver is. Nostalgia is one thing, business is another.

I have also heard that 1000 oz bars are not as easy to sell because they often have to be refined first to ensure purity. Since these are normally industrial units of silver, if you end up with one and try to sell it then it would be considered outside the chain of integrity and sent off for refining prior to sale.