Lots of thought-provoking stuff.

Solo unaccompanied singing.
Unaccompanied harmonies sung in small ensembles.
Solo singing with one instrument accompanying.
Small-groups singing accomapnied by one or more instruments.

I started off singing unaccompanied because I could sing but not play anything musical. Campfire songs, music hall, shanties, ballads, jingles, forebitters, marching songs, counting/repetition songs; all were grist to the mill. Solo, you were forced into listening to how others made the song work and then put your own efforts into making it work. While I didn't do gigs continuously it was easy enough to vary the pace, style etc and break up the pattern with the occasional recitation. I suspect the story-telling used by some performers between their songs is their subtitute for recitations.

Then I got involved with Pageant, six people from Victoria, Sydney and Canberra, who were all solo singers (two sopranos, two tenors, two baritone/bass) and only the tenors could play instruments; free reed ones, as it happened. We felt that the best songs were ones that stood without accompaniment by instruments, so we sang unaccompanied harmonies. Much, probably most, of our repertoire was UK in origin (two of us were originally Poms) and American friends who've heard our stuff compared it favourably with the Voice Squad. We did lots of gigs for whole evenings/afternoons and the variations in style provided by solo and group singing were easily supported.

Most of us were also dancers and an accident of timing at a National meant we had to become a bush dance band for a TV spot demonstrating some colonial dances. We didn't want Pageant's reputation sullied by a wonky band performance so we changed our name. The broadcast started Higgins Municipal Bush Band on its way and also started us singing to solo and group instrumental accompaniment to some acclaim.

Personally I still find it easier to sing unaccompanied but I'm lucky enough to be able to both hold pitch for an extended song, as well as hold a melodic line against another equally strong melodic line. Some very good singers find both difficult but their vocal qualities still make them superb to listen to. As many melodeon and Anglo players know, these instruments breathe differently to people so I have a limited ability to sing while playing. Interestingly, I find it very easy to call dances while playing the tunes I use for various dances; I suspect I'm using the calling as a singing accompaniment to the playing. I've not heard too many others criticise my paying the way I do.

Cheers, Rowan