What's The Most Value-Effective Bullion To Stack?

Value effective to me means considering both the buy side and the sell side. Therefore, US 90% is my choice. There is a much greater chance of acquiring at or below spot than any .999 product
(even XF+). It's highly liquid and let's say you sell at spot not unlikely), then your return pretty much perfectly tracks the underlying silver price trend, which is a core pillar behind why most accumulate silver. I have ASEs too, so I completely understand that route as a preference.