Hey, welcome to dof.
The royal dragon is definitely the strongest. The haunter and frost dragons are special dragons that you can only get from events, they aren't all that strong, but I THINK that they are the only ones that always respawn (there was a thing about changing how dragons work a while ago, not sure whether they kept special dragons as immortal or not).
For storage space, there are some storage upgrades (at the main buildings for human and elf, and at a hut for orc), but after that you can give some resources to your armies (certain units, like wagons, ogres, and the elf tree-things, can carry a lot).
Anyway, hope you like the game.
That was so funny, I laughed twice.