Favorite of all time is really difficult. I tend not to stick with one album for more than a couple months. That said, here are a couple picks from current & older rotations:

The sheer intensity of Brittany Howard's voice pretty much covers this one for me. I saw a live performance broadcasted on PBS and it was absolutely incredible-- I was in the middle of something, but ended up in front of the TV for over an hour, transfixed.

IMO Whitacre writes some of the most beautiful harmonies there are. I heard Colgate's Chamber Singers do this piece and it was what got me back into choral music.

It's hard to call this one of my favorites of all time, but I first stumbled upon it about a month ago and I've had it on heavy rotation ever since. Something about the beauty of the lyrics and the tight, twangy harmony laid bare.

I come back to this song whenever something really terrible has happened. I played it on the radio show in the days after the Paris attacks. It's one of the most beautiful expressions of hope I've heard.