Well, in my opinion i believe out of myth and balance, balance would be the best choice. The reason why i say that is because myth is based on attack and as death you have all the attack spells you need with healing. Myth just gives you extra creatures that will most likely just get in your decks way. With balance you got some decent buff and debuffs you may use to make your opponent lose guard and attack while you work on destroying him with your death spells. I myself have a death character and i chose fire as my second class. I never use my fire cards at all because death does all the work for me. With death its better to get a class with support spells then with attack. Also don't forgot to get the tri blade spell when you reach level 25 at the krokosphinx balance tree. Hope this helps and good luck.