Agreed ... each has its uses. I actually had an issue while voting, since only 5 checks are allowed. I've basically used all of those, including "other". Where other may have been an external file, or a database, usually due to something external to ACad also requiring access to the data.
Globals & black-board are nice to use for things like settings. Since you can have them shared across dwg environments or or only relevant per dwg, sometimes you want one of those or both - reasonably simple to achieve both scenarios. IMO they're pretty much interchangeable and depends how you like to do things.
For keeping data / settings permanent there's also various ways allowing different use cases. Perhaps you want to store some relevant data only pertinent to a specific DWG, in which case a Dwg-Props or Overall Dictionary is adequate. If only to be part of a specific object in that DWG, the both XData and Object-attached-Dictionary is the way. Usually Dictionaries are easier to use if you work with vla functions, otherwise they become a bit cumbersome when working through DXF codes (too many nesting levels).