I will rank them according to my rating.
1. Black Dragon
2. Lava Dragon
3. Archangel
4. Titan
5. Emerald Dragon
6. Archdevil
7. Spectral Dragons
I would like to add that if the Nival developers don't make a DECENT alternate upgrade for the Spectral Dragons (i.e., so that they become on par with other Dragons), I will be very upset.:mad:

Dear Lord Vampire, I suggest you switch to playing as the High Elves; they have the tactics you like – small growth, but a lot of power. Necromancers rely on numbers, which is why their units are weak, and even the Spectral Dragons are worth their 2900 gold + 2 mercury. The most annoying thing is that Emerald Dragons cost 4700 gold + 2 gems, while Black Dragons cost 4500 + 2 sulfur, which is completely unfair, considering the abilities of these two creatures.

My humble opinion:
Based on appearance:
1. Black Dragons
2. Spectral Dragons
3. Emerald Dragon
4. Lava Dragon
5. Fallen Angel
6. Archangel
7. Titan
8. Archdevil
Based on tactical abilities:
1. Black Dragon
2. Titan
3. Lava Dragon
4. Fallen Angel
5. Archangel
6. Emerald Dragon
7. Archdevil
8. Spectral Dragon