Reply: I'd recommend using two Crown CM-700 cardioid condenser microphones (or a CM-700MP matched pair of microphones). For starters, place them in a stereo mic bar, angled 90 degrees apart (+/- 45 degrees from center) and spaced 8 to 11 inches apart. Use an extra mic-stand boom so you can raise the mics about a foot above the head height of the back row of singers. Angle the mics down to aim at the back row.
Place the mic stand 12 feet from the choir, make a test recording, and listen to the playback. If the sound is too dry (lacking hall acoustics), move the mic stand 1 or 2 feet farther away and try again. If the sound is too distant or muddy, move the mic stand 1 or 2 feet closer and try again. If your room acoustics are poor, you could mike the choir fairly close (less than 12 feet away) and add artificial reverberation with a long reverb time.
An alternative stereo miking technique with less-sharp imaging is two spaced CM-700s. Place each CM-700 on a mic stand, raised above the head height of the back row, aiming straight ahead, angled down toward the back row, and spaced 3 feet apart.
If feedback or audience noise are issues, you might want to mike the choir closer than usual – maybe using 4 spaced mics each 3 feet from the choir and panned into position. That’s not really a true stereo recording but it might be your only option.
Then, to get the room sound back, use a high-quality reverberation plug-in in your audio editing program, such as Lexicon Pantheon reverb (available for Cakewalk Sonar Producer) or various convolution reverb plug-ins.
Close miking rejects the audience noise but also reduces the room sound (reverb). So you need to create artificial reverb with a reverb plug-in or hardware reverb unit. Actually, this can sound really good, even though it is not an accurate representation of the hall you recorded the choir in.