YOu may encounter different approaches to how players interpret fields with several pieces of data in them. Which means that there is no best practice.
On the other hand: try to find out for which purpose you need that separation most. If you do not really need separate fields but you can tolerate all pieces of data in 1 string, then go for the semicolon-space option. This shows you all the (e.g.) artists in 1 field and you don't have to fuss around with merging the fields if you want to write a new filename. Also, by avoiding any kind of slash (forward, backward, single, double) you do not run into trouble in respect to file system conventions and special characters.
And should it happen that you need a special separator, you can use MP3tag's functions to replace semicolon-space with that what you need.
See also here: