Who do you generally get rid of, excluding the "commoners." I, personally, try to keep all the "special" characters. I don't know why, but I just have to keep the "one of a kind"s. This does pose a problem when trying to breed monsters though, since there's a total of 16 "special"s (including the three you get at the beginning of chapter 2 (Rad, Alicia, and Lavian, I think their names are), Boco, and Byblos), and you can only have 16 units.

I always get rid of the first group you start out with when I get enough "special"s to fill a 5 party team.