Why does ORTF become the "go-to" in every situation that I walk into where there are a lot of variables that I have yet to hear? Because it works. Amazingly versatile pair. Not to say that after I know the performers and the space that I can't up the level of the recordings with a different approach, but if I have to put something up and expect it to produce a good result, ORTF seems a good choice.
FWIW, I have been using a Blumlein pair on choir and accompaniment lately. I use the Royer SF-12 stereo ribbon and it sounds wonderful on mixed voices.
Douglas Tourtelot, CAS
"Recording sound is merely problem solving. Solve one problem and move on to the next"