What would you consider as "fair" line distribution?

[BlessMeAchoo]

I think to be fair it should be based on both position and the number of lines each member gets. Obviously the main vocal should get the most lines, but that doesn't mean that they have to have disporportionatley more lines so that some members only get like 1 word in a song. Giving the popular members more lines would just make it even harder for the less popular members to get more recognition.