Well it all depends on what skills you want for your units and what class you want them to end on. For example, my knight's reclass options are Monk and Shaman. I don't intend to reclass into shaman, but picking it gives that unit access to Druid later on (which I do want). All the other skills I want are from Monk, General, Bishop, and finally Holy Knight (my ending class). This is so that she becomes a massive defensive support unit that also excels at taking down risen and other monsters.

You think up some ending units and what their role on the team is, and then figure out what classes they have to go through to best fit that role.