We're looking for a omnidirection microphone- actually 2 - which can pick up a 20 voice choir either hung from above or on mike stands. This application is for a church. Can you give us a recommendation?
If these microphones are going to be used for sound reinforcement, you should not use omnidirectional microphones. Unidirectional, specifically cardioid, pickup patterns will accommodate choirs if they are postioned correctly.
Please refer to this site for ideas on microphone positioning and model numbers: How do I mic a choir?