Depends on what you're growing.
The basic premise is depending on genetics, you want to target different substrate depths. So psilocybes do great between 4"-6" of substrate depth when doing bulk casings. Size of container depends on the space you have available. If you're doing a shotgun fruiting chamber, something that can accommodate 9"x9" cake pans is perfect. A monotub, you can scale up to 50L units before running into issues.
Pan Cyans like a thinner substrate layer.
Oysters like logs and bags.
Lion's Mane, Shitakes, Maitakes, Reishis all like bags or logs.
Like i said, it depends.