Best of the coin capsules?

They're not, they're flat, and the high points of the coin do touch the holder.

I say no, absolutely not, and for several reasons. Proper coin storage requires that inert materials be used and the cardboard is most definitely not inert, it is saturated with sulfur when it is made. And sulfur can and will cause toning, often unsightly toning. Then there is cardboard dust, that all cardboard produces. These tiny pieces of cardboard can and do get on the surface of the coin, and as it decays over time it can and will produce spots on the coin. Cardboard dust can also hairline the coin. Then there is the mylar cover, it is so thin that a coin can be easily be dinged/dented and or scratched right through the mylar. Lastly a coin can and often does move around inside carboard 2x2s imparting additional wear to the coin where the mylar touches the coin. This movement is also what allows hairlines to be caused by cardboard dust.

Bottom line, as listed above there are several reasons why cardboard 2x2s are a bad idea for coins. The one and only good thing they have going for them is that they are cheap.

Proper storage requires several things. 1 - inert materials. 2 - the holder must hold the coin securely and prevent any movement. 3 - the holder must protect the coin from outside contact. 4 - the holder must limit air flow from getting to the coin a much as possible.

The only holders that do all this are the hard plastic holders, of which there are two basic types, the Air-Tite style and the slab style. Several different brands of each, but two basic types.