to be honest in a fair fight I think that Archimonde would have defeated Kil'Jaeden. That is because Archimonde greatest feat was his powers as a warrior, where as Kil'Jaeden was best known for his elaborate schemes. Would Kil'Jaeden ever allow himself to get into a fair fight with Archimonde? Not a chance. So it really depends on what you mean by power. If you mean raw physical strength and the potency of their spells, then it would very much depend on whether demons are immune to the Frostmourne or not. If you on the other hand include their armies, then the Lich King doesn't even come close to anyone on that list.