I would generally agree with this. If you can buy "junk" silver for the same money, choose coins that have the highest chance of being collectible in the future. To me, that means all coin designs not in circulation, or bu coins. I aim to buy half dollars if possible as well, since everyone likes larger coins.
I collect any and all 90% silver coins. I also buy them for investment, the ones not in circulation. But I prefer to buy as many silver dollars as possible, mainly Morgans. You can buy these in junk grade as well as other junk coins. They're large and contain .7734% silver.