Are there hidden attributes to the classes or just what is listed?

Aside from premium classes it would just be better to go with the Elemental Forest Princess since she gets the most energy. Low cap, but while you are playing you gain it faster - if you never let it max out that is way better than most of the other classes.

Who would bother playing a Dwarf when the Archer gets the same gold, twice as much energy, and over two times the energy cap. And the Barbarian is even worse than the Dwarf.