I went through this decision process a few months ago and came down to Compose, Type, Work, Conductor (alphabetic) though I gave some thought to Composer, Type, Conductor, Work
Composer: Sibelius
Type: Symphony
-Symphony 1
--- Davis
--- Karajan
--- Maazel
-Symphony 2
--- Davis
--- Karajan
--- Maazel
type: Tone Poem
-Swan of Tuonella
--- Kamu
--- Karajan
--- Ormandy
-Tapiola
--- Kamu
--- Karajan
--- Ormandy
etc.
When there were multiple composers on an album I tended to group by whomever was predominant or who was side 1 track 1. However I did have a couple groups like "The Russian Five" (Dui, Borodin, Balakirev, Mussorgsky, Rimsky-Korsakov). And I did end up with a category of Unclassified and tried to keep that small.
The actually doing was something of a "rebuilding the boat while at sea" riot:
