Was slightly tricky to choose but after 5min of considerations between two of'em I made my choice.
I only read the popups since 5000 words should be enough.
The ones I excluded (from first excluded to last) and why:
- Til deaths do us part - I'm not sure I like the ability to get unique Firespells from a quest. It also has a lot of conditions. It sounds complex and hard to balance. I like the population sacrifice though
- The Rod of Mages - Standard comboartifact campaignquest from Heroes of Might & Magic III. There's nothing that stands out
- Forces in exile - I like this one. You know what you're getting (you can check all champions/heroes stats and equipment right?) so you know if it is worth the risk and resources it demands. having to go to another factions lands first to finish the first part of it is also something I like since you have to take that factions diplomatic standing with you in account. Then having to do two other steps is acceptable. But you know what you get.
While I didn't like Til deaths do us part and The Rod of Mages, Forces in exile is good enough, though it loses out to the last two quite easily.
Finale
Dark Rising starts out completely unaware, like Diablo II 
Then you get the Den of Evil quest from Akara who tells quite vividly about that evil place and asks you to go slay the evil of the underworld.
Anyway, I can imagine the epicness of the quest (if creatures on the map could make noise and stuff) where the forces of darkness starts quite small but quickly grows stronger. Too fast I'd say but we can't drag it out too mucjh! 
I also really like the camps spawning raiding parties. It should work like Master of Magic where raiding parties are spawned whenever the creatures within grow beyond some number. It worked kinda the same way in Warlords BattleCry III. Max amount of lairs that constantly spawn monsters was the most exciting game I played.
The quest could take quite long to do since it's described WAY too epic to be completed within two weeks or so.
I also feel that the quest could have more possibilities (like if you're an Empire):
- Ally with the mighty dragon so she attacks someone else. Would require LOTS of work to make an alliance lengthy and reliable, like having Darklings & Darkling villages under your command, paying her once in a while and giving her a mate! i feel that there needs to be a slider or something that shows how trustworthy the alliance/cooperation is so you don't wake up one morning and find your Empire burning, your Capitol sacked and your Darkling horde turned against you simply becaus the dragon "changed her mind".
If you defeat some of there forces first, your relations will worsen and the more you destroy the worse they will become.
Kingdoms, however....which should have a very hard time recruiting Darklings could kill as much as they wanted and threaten and bribe the dragon to attack someone else. This should include the ability to tell the Darklings to set up camps somewhere else.
That became long, but all things considered, I really like this quest!
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Demon Lord is cool and plays with a classic story, the opening of something that should have stayed CLOSED!
I see potential for this quest as well. Mastery in Summoning magic could open the gate again and shackle the demons that pour forth. Perhaps a limited control over them. The magic that shackles them only work for x turns or something?
I dabbled between Dark Rising and Demon Lord for 5min but in the end:
DARK RISING WON! 
I got one request though, Kenata. Change avatar! Having some fuzzy monster preparing a toothbrush with glue or whatever it is while his sitting on the toilet just looks weird!
...Maybe I should have brought up this change avatar business BEFORE I voted for your questentry 
