Some factors are obvious. Some characters are clearly supporting characters, in that they are there as someone with whom a main character interacts, like the Galeckis. Other guest actors and supporting characters carry episodes and storylines and stand out on their own. I wanted to put Mr. Entertainment higher, given that his character was prominently featured, and I really liked him, but he was only in two episodes, and was featured more like a guest star, sort of like Betty White as Captain Gloria Neal... it's tricky! So I'm not going to worry about it too much. My aim is to simply have a listing that jogs viewers' memories, and reminds them of how many great acting performances and interesting characters made St. Elsewhere worth watching.
Remembering Betty White's appearance makes me think I'll probably add notable one- or two-off guest stars as well. Eventually.
In other developments, I've also changed settings so that comments don't require admin moderation before publishing. I'll get any offending ones afterwards.