It doesn't matter what faction it's for, if it's DLC, Main, Unmarked or Side.
What matters is this:
* It's writing.
* It's choices.
* It's consequences.
So which quest is best designed in New Vegas?
(And yeah I know it's unusual for me to create threads, especially this many in such a close order, but we since we don't have much to discuss we can always just rehash old stuff.)
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I like Come Fly With Me.
Not sure if I'd vote for it as the best quest, but it has tons of choices in it.
First, you can choose whether to persuade the information out of Manny to not even do the quest. (1)
Or you can look at his computer for the information. (2)
If you get the quest, then you can choose between entering the front of REPCONN or sneak around the back. (4)
After that you get to talk to Jason or kill the entire bunch then and there. (6)
If you don't kill them you go down into the basemant, there you can do multiple things as well.
You can choose to just kill Harland, or you can accept his request. (7)
Then you can choose to kill the Nightkin, or help them out. (8)
You can sneak past the jailguard Nightkin and get a key out of a desk to get down to Harlands girlfriend or you can just kill him and take the key. (10)
After that you can tell Harland what happened, get to the information on the computer and tell Davidson that there are no stealthboys there.
Then you have to get crap for the rockets, with one of the two fetch quests you can either buy a load of those toy rockets at the DinoBite shop or get the Isotope agent outside of Clark Field. (12)
With the other you can charm Gibson, kill her or pickpocket the key to the box containing the thrust controller. (15)
Then you can convince Chris to sabotage the rockets or you can tell him that it's not the right thing to do. (17)
And finally, you can choose to crash the rockets or let them fly off. (19)
I know I'm counting the little things too, but there is a total of 19 choices here.
From the big things like choosing their destiny, to little things as what entrance to take into the building.
It's theme is a bit ridiculous though but it's writing is good, despite somewhat lulzy.
So Come Fly With Me is a good example of this.
You can go the pacifist route, choose to kill everything, choose to be evil in a more clever way, be good and/or be biased.