I have a level 50 Spica (non-CC because need Silver Archers), and was wondering what the best use of Demon Crystals is now. More Spica for CR and Skill improvements? The Ninja or the Samurai? Maybe the Mage? I'm not quite sure what would constitute a "good" use of Crystals and what would be wasteful.

Admittedly I'm not sure I'd use most of them other than Spica, the Mage may have seen use if I didn't get Odette to 31 Cost. But I'm not the best at determining what would be a solid army capable of handling whatever gets thrown at it. That's a question for another thread however.