So, I have a bunch of cards stored in top loaders and old school screw down cases. Most of these are older (normal thickness) cards that I want to keep in cases (either due to value or just because they are special). Many have been in the same case since the late 1990s.

Right now, it's a mixed bag of case types. I'd like to slowly transition them into a more uniform type of case and make sure they are stored in a manner that is safe for the card. What is the best type of case in which to store cards?