Hi Bill,
One of my friends is a jazz singer and years ago, I asked her "which is the best key to use for singing" her reply was:-
"Generally B flat or the key of F is used for group singing, but for soloists it would be the singer's choice" (her choice was B Flat).
I also recall attending an Organ Concert where Peter Hayward was playing and in the interval he gave a demonstration of what he called "magic notes" that 'ear-players' like to use. They were all black notes and he said the majority of audiences also like the black notes because they seem to suit everyone's voice tone "neither very high or very low" I think he does have a point.
Also, don't forget the Transpose key! This can be very useful when you think the tune is too high or too low for your 'live' audience.
If you have any of John North's KN7 Christmas Party sets, most of them work just fine with any audience because they are designated tunes.
Hope this helps and a Merry Christmas to you and yours Bill and also to all our other friends on this Forum. May we all have a healthy and peaceful New Year.
Audrey