Don't remember the name of it, but I would say the quest you do for Red Lucy. I may be a courier, but damnit, I'm not your personal delivery boy; you want eggs? Go out and get 'em yourself...or are you too chicken? :down:
EDIT: Bleed Me Dry.
The fetch quests are really to get the player travelling around the map to places you might not otherwise discover, so they're useful early on and fairly quick if you've discovered everything. I like Bleed Me Dry, it's especially good for challenge level, locations and rewards, you get as a reward a hunting rifle, hunting revolver, Dinner Bell (one of the best guns in the game), 1650 XP and up 6400 caps. You find, assuming you haven't already looted the locations, the AER Prototype, a hunting shotgun, a hunting revolver, 12.7 pistol, 12.7 SMG, a Fat Man (maybe 2) and Mercy and Power Armour depending on which location you go to. And that's just the highlights.
Trouble with all the fetch quests is that they're a bit of a slog after a couple of playthroughs and BMD in particular is a lot of work just for a good shotgun.