CDDB searches will return some terrible tags. The worst are with dance compilations where there is an original artist (a composer) and a remixer (artist).
Main artist plus guest: A tricky one. Case in Point: Tom Jones "Reload"- 17 songs, each with a guest artist. I entered "Tom Jones & _" as the artist tag for each song, which gave me 17 artists. This is a pain to scroll through, plus the focus is supposed to be on Tom Jones, as it's his record. The way I solved this was to add "(Feat. _)" to the end of every song name tag. This gave me 17 Tom Jones songs, but I kept a note of who he was performing with. This is a trick inspired by the sleeve notes on dance compilations.