Which Armageddon's Blade campaign do you like the most?

I've just paused on the "Dragon Slayer" mission and would like to know: 1. Is it worth taking the Ring of Diplomacy in the first mission? (I didn't take it and I regret it.) 2. Which mission should I choose next? (I played with the Magic Dragons, but there are quite a few of them in one place, and they keep defeating me... I was thinking of building up an army, but I'm not sure. Maybe a different tactic is needed, or should I go to the Rust Dragons?) P.S. "Playing with Fire" is difficult (compared to the others, except for "Dragon Slayer" of course) and interesting; there's something about it that's captivating, which is why I like it the most.