Well, if you have 2 crown of chaos, armageddon is better than black hole.
And armagedon still the most damaging mass target spell without any bonus from items. With items it will do 50% more dmg than black hole, probably more, i forgot about this.
One thing strange about armagedon is it deal astral dmg, but +fire spell dmg increase its dmg. If i remembered right, it is possible to reach more than 10k dmg with your armagedon by wearing necklace of firestorm + other similar items. Very scary if you ask me
Another way to use armagedon is using turn back time, but it is too mana consuming. But if i remembered right, someone actually found the correct items + skills + units to efficiently do armagedon+turn back time combo, i only remember what is the unit though. Yep, as you probably already guessed, it is the green dragons.
Hmm, if you use green dragons, i think it will solve your mana restoring problems.
KB TL armagedon is better i guess, because if i remembered right, when you use armagedon, you gather so much rage, then you can turn back time your green dragon, turn back time in TL is rage spirit ability, it is not too mana consuming as in AP/CW. But then again, there is a possibility that CW can provide 2 crown of chaos.
As for the quest, i give up.