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

I'm currently stuck on the "Dragon Slayer" quest 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?)

I chose the quest with the Rust Dragons first because I kept getting crushed by the Magic Dragons... and it's best if you have some leftover troops after the first mission, like Titans and Nags. By the way, choosing the right magic will help you keep them - it's best to have Berserk, as it's deadly on magical lands.
I usually took the Ring of Diplomacy... although, to be honest, there's not much difference. It just opens a small treasure chest on the next level.
But the campaign is really engaging, I've played it many times :)