Oh god, such a hard choice. As SnapSlav said almost every quest in FO3 has some retadred elements, choosing the worst isn't easy. I'd say that the worst two for me were:
-The Arefu quest. So you track down this bunch of loonatics that terrorized the small settlment, killed their brhamins (not a small loss) and, as far as the Arefu inhabitants know, killed the West family. You talk with them and their leader tells you that they have this condition that comples them to eat human flesh but he managed to convert it into simply drinking blood. So now you have three options.
A)Kill them all. This is treated by the game AS A BAD THING! Killing a group of weirdos that harm innocent people in an lawless eye-for-an-eye society is bad? And to top it off the option is bugged and it can cause the inhabitants of Arefu to attack you
for killing the people they wanted dead!
B)Tell them that it's their problem and should leave Arefu alone otherwise you'll kill them all, and if they really wanted blood so bad they could chase raiders instead of settling for the easy target. Oh wait, no. This option makes too much sense so it's not in the game.
C)You tell them to leave Arefu alone but they say they can't and Arefu
has to give them blood to help them otherwise no dice.
And this is treated as the good option! Oh, sure, you can sweeten the deal by having them provide security for the settlement but that they have the guts to pretend help from a settlement they harmed and terrorized and this being treated as the good option is mind boggling. Even more absurd is that Arefu accept their conditions! Again, the "vampires" terrorized them, made a woman go insane, killed their stock, killed the West family and abducted Ian (the truth was never revelaed to them on this). And they are totally fine with it.
If there was a "happy ending" quest with a surprise twist it should have been this one, not the Tenpenny one with the ghouls. You should have returned a few days later to Arefu to find all the "vamipres" slaughtered in a trap by the Arefu citizens. But I guess it would have ended being unnoticxed since you don't have any real reason to return to Arefu once you complete this quest.
Oh, and the final kicker: if you return to Lucy West (which was sooooo worried for her family and brother) she doesn't ask anything and you can't say anything of what happened. Fantastic!
-The android quest. So this android-needs-surgery thing gets your attention and you manage to find the surgeon. After knowing all the details, knowing that the andorid chose of his own will to forget everything but that his past memories are still within him you choose to make him remember who he really is. Wait, what? How does this make ANY sense? The only reason given is "you would want to know if you were an android". Did the Lone Wanderer forget that
he chose it himself to forget? And, with people searching for him, he is actually more safe not knowing? Regardless, your idiot character meets with the android and says the password that unlocks his past memories. After a painful-to-watch scene (the animation is horrible here) the andorid rightfully asks why you made him remember his painful past and rewards you by giving you his best Plasma rifle. WAIT, WHAT!?