I listen to an astonishing amount of choral music. This music involves tons of different ensembles, conductors, and types of music. In all of this listening/learning I tend to listen for specific things, but more often I listen for CHORAL INTONATION.
I believe that as a conductor this is what we all try to master. Depending on your group and the style of music, your intonation will change to fit the style. Well in my search to find the best sounding choirs I can listen to, I have come to realize that the best sounding choirs have 1 element that helps make the ensemble intonation sound amazing, and most people probably overlook this when listening to choral groups. For Example; Dale Warland Singers are known througout the United States as “An Amazing Choir” especially their sound. University of Miami Frost Chorale directed by Dr. Jo-michael Scheibe i believe is one of the best choral groups at the collegiate level. Other choirs would be Ars Nova Singers (Thomas Morgan), The Esoterics (Dr. Eric Banks), Choir of the West (Dr. Richard Sparks), Seattle Pro Musica (Karen P. Thompson), University of Michigan Choirs (Jerry Blackstone), BYU Singers (Dr. Ronald Staheli) etc.
What I have determined by all this is that all the best sounding choirs have conductors who are composers or arrangers/editors. I believe that with those skills comes the ability of giving finer detail to Choral Intonation then conductors with conducting degrees. Now, dont get me wrong there are amazing choral conductors who are not prolific composers/arrangers in the United States that I have heard and greatly admire; Dr. Richard Sparks (Choral Arts NW, Pro Coro Canada), Dr. Joe Miller (Westminster Choir College), Peter Phillips (Tallis Scholars), Dr. Greg Vancil (Seattle Bach Choir), and there are a few more.
So just a thought that if you listen closely to a choir conducted someone who works as a composer/arranger, and then listen to the same song conducted by a different choir with a conductor who does not compose or arrange music you will notice the difference in Choral Intonation (with some exception to the great Choral Conductors listed above (sparks, Vancil, Phillips, etc).
But all of those conductors that I have listed are what I define as the best choral directors.