From fallout 3 my favorite NPC is the Goth Girl Bitter Cup. I wish they would have done more with her in the vanilla game, she was so interesting.
In New Vegas my favorite is Cass and Boone at a tie. I like both characters and their back stories are deep. I think Boone might beat out Cass by a little. His story is so sad.
We are the hollow men We are the stuffed men Leaning together Headpiece filled with straw. Alas! Our dried voices, when We whisper together Are quiet and meaningless
As wind in dry grass Or rats' feet over broken glass In our dry cellar Shape without form, shade without colour, Paralysed force, gesture without motion; Those who have crossed With direct eyes, to death's other Kingdom Remember us-if at all-not as lost Violent souls, but only As the hollow men The stuffed men.