Suggest best media for terrarium?

[buffalo]

I've been making terrarium for years and use potting soil, as we know all soils not made the same . As a result some terrarium with soil struggle while other do exceptionally well. I've heard of terrarium using just pea gravel, some with sphagnum moss etc ( I've tried sphagum moss i usually get mold issues. Let me know what you find most successful in vivarium and terrarium for soil media.