Opinions On Snap Lock 2x2 Cases Vs. Air Tites?

I'm not aware of any long term storage difference between round and square capsules. One company says their capsules are "air tight" but I don't think any of them are 100%. Even NGC, PCGS etc slabs are not air tight. If stored where there is high humidity, cigarette smoke etc graded/slabbed coins can tone over time. It's good to store coins in low humidity. I have a dehumidifier in the room where I store coins in a safe.

I use acid free paper flips for my ancient and some modern coins that are okay to handle. It's easier to take them out and hold them which I like to do and it doesn't harm them. I write descriptions on the flips. I use round plastic capsules for modern coins/bullion I should not touch much, fingerprints and such, just personal preference. To label the capsules I type description on piece of paper and tape it to the capsule. This may sound tacky to some but works for me. I usually put them in coin storage boxes or food storage containers sorted by categories. My collectible classic USA coins are either in round capsules or graded/slabbed.

A lot of collectors like to use coin holders like Dansco and Whitman albums. These are great for those who collect years of a certain denomination, type set.

@Brandmeister I've used both Air-Tite and the square type snap-lock I think (see picture). I find the air-tites are a really nice holder but tricky to re-open trying not to damage anything. I find I have to use a utility knife type blade to separate the two pieces of plastic. The ones in the picture below are easier to open but look a little dull. I also use the 2x2 carboard flips and mylar flips for most circulation coins. Like you I'm trying to find the best match between protection, access, value, labelling, etc.. It's not easy. Good luck