Desert Dancer, I totally agree with your OP.

I live to sing, preferably a cappella with others. It's utterly the best way to spend time with people. The only criterion I'd add to yours for music selection is one my quartet (and the a cappella chorus to which I belong) likes: We go for songs with a clear story, and fairly simple emotions. If the emotional story is too subtle we find it can be harder to clearly convey the change from one feeling to the next. Possible, but more difficult.

Like you, when at last we get it, "it" being the mix of accurate notes, matched vowels, and the joy of the shared undertaking, the feeling is wonderful!