Agreed on Thunderblight being the hardest dungeon boss, which is partly why Daruk's Protection might come in handy for first timers. I also think that the events leading up to it are the most involved out of the four DB quests, and doing this quest includes a permanent change in regards to enemy...
Probably this:
Medoh>Ruta>Rudania>Naboris
Medoh is in the upper left corner(which is what usually denotes that something is supposed to be first in something ordered like a list), you can see it from anywhere, and it's in a plains-like area which is a common starting area in games, and unlike...