I think my question is sort of on the subject: which of these are meant to be sung by the entire congregation, and which are meant to be sung by only the reader? I go to matins many mornings and there are only a few of us there (I am a catechumen so a lot of this is new to me, btw), and our presiding priest assigns us each something - theotokia, troparia to the saint of the day, or the third one (ummm...the other day it was the holy cross, and a couple days later it was just more troparia to the same saint because it was the Hierarch Gregory). Then there are ones we all sing together, but I am not always sure I'm supposed to be singing (the irmos, for instance). I just sing, mostly, and I figure he'll tell me if I'm not supposed to be singing.
Hymns that follow a pattern or that are widely used are good to be sung congregationally. This would include the Apolytikia and their accompanying Theotokia, the Troparia that follow "Lord, I Have Cried" (the Vesperal Stichera) and "Let Everything That Breathes Praise the Lord" (the Matins Stichera), the Kathismata of matins, the common canons (and the Katavasies), the Aposticha of Vespers (and of Matins, if you actually do them - most don't), and all the hymns of Liturgy.
What shouldn't be chanted? Well, everything should at least be sung to oneself. But what shouldn't be "belted out" would mainly be the "unique" hymns (Idiomela), which include the Glory hymns of Vespers and Matins, the Liti hymns, hymns that replace common hymns (like the Cherubic hymn or Communion hymn) for major feasts.Addendum
- Something that many people forget is that even when singing congregationally, one must remember that they are not leading
the singing from their seats - so they shouldn't be singing at full blast into their neighbor's ears. The Cantor / Choir are leading, and they should indeed be chanting loudly so as to lead. If people in the pews chant as if they are leading, then the other folks around them will be less able to hear the Cantor / Choir and thus less able to tell if the person next to them is chanting correctly. There are many scriptural references to the differentiation of roles and talents, and we must remember that.