About three quarters of my discs (over 2000) are classical. I decided when starting with OCD a few years ago, wherever there was a conductor, to use the conductor as the artist. I cannot see any reason for using using the composer as the artist as some people seem to do, when classical layout allows for Composer, either for whole album or selected tracks.

I would only put orchestra as artist when, as sometimes occurs, the ensemble is conductorless.

If it is a compilation disc with two or more conductors, the album will have "Various Artists" and I would use the conductor as track artist - easy to do with multiple track selection via "View Track" on right click.

In the case of a single singer compilation - eg Maria Callas doing opera highlights with various different conductors and orchestras, it seems more logical to me to use that singer as the artist and to put the conductor into track Credits, since it is set up as an album showcasing a specific artist.

Ever since artist collaboration has been possible both on album and track properties I have used this for concerto discs to be able to include both soloist and conductor as joint artists eg Bernard Haitink & Alfred Brendel. I have even gone back and done this retrospectively to concerto discs I entered before this was possible. The advantage of this is that if you select Alfred Brendel under Artist it gives you both piano solo and piano concerto performances.

Obviously, once you've arrived at a particular method which works for you, you just have to stick with it and be consistent.