The choirs at my university sing in straight tone, because the conductor says that the pitches are much purer, the chords are much clearer, overtones "shoot out" much more, and that it's actually not uncommon practice in Europe, you just don't hear it quite as much in the United States.
Here is an example of one of our choirs (I do not sing in this one) singing in straight tone, and pay attention to the very long held chords. I don't feel they'd have NEARLY the same effect if the singers used vibrato.
I'm afraid I've been spoiled, because now whenever I hear other choirs sing with vibrato, I feel like the chords aren't very clear, and sometimes I don't even hear the third or fifth or seventh or whatever other important scale degree of the chord clearly.
Yet still, some choirs, like the Latvian youth choir Kamer sing with vibrato, but I like their sound very much. Is it in how it is used or how much of it is used, or what?
What do you guys think?