Greek Cities and Dacia always seem to be in trouble, as well as Carthage and Numidia (though one of them generally dies and the other one just gets tiny.) Selucids are killed about 60% of the time, and when they are, usually Pontus and/or Parthia are.

I've never had any problems with Germania dying. They get small a lot of the time, but I don't think I've ever had them killed off without me helping in their death.