The most advanced faction is the one with black dragons. Due to their advantage in the number of ranged units, and their main feature is Black Dragons, due to their immunity to magic. Also, the "Inferno" Castle is a strong faction because of its Efreet. 60 upgraded Efreet are better than 15 Devils. The "Tower" faction is also strong; it is strong because of its Nagas. They have weak Titans, but they have many ranged units, and Djinns are equivalent to Efreet.

There are no good heroes in the Dungeon, so it is immediately ruled out. A large number of ranged units is good against the AI, but against humans, it is better to have minimal range. If a unit shoots, it loses in something else, usually in defense and has a penalty in melee combat. 60 upgraded Efreet may only be better than Wyverns, and they lose to the rest. The only thing that pleases is the fire shield and the movement range. The Tower is too expensive. Titans are not good. But I agree with you about the Nagas. Not being affected by the Slow spell is really a strength. It is best to play as Humans. It is the most optimal faction, and the hero there is the best - Adel. Diplomacy!!!