Angel

This is the poor man's druid.  They are relatively easy to acquire if you sacrifice honor badges or "buy" gems.  I think the Angel is only kind of useful, but I have one that I've levelled up into the 60's.  My plan is to keep the Angel until I get the Druid.  At that point, I'll stick her in my arrow tower in order to expand it's range.  Thus, I think the Angel is worth having especially once you reach the stage where you want to farm the skull battles in the dungeons using only your heroes.