This is incredibly hard. There are a lot of writers who I think are fantastic. Cutting it down to 3 is cruel. But those are the rules, so here goes.
enigmaticblues for the "Alive" saga and "Cast Me Not Away". Simply exquisite; wonderful explorations of Spike's emotions and examinations of what makes a sentient being truly a person.
missmurchison for "Quick and Bitter, Slow and Sweet" and "A Glorious Morning Have I Seen". QAB,S&S is delectable Spike/Tara, sweet and funny and tender and sometimes heart-wrenching, with wonderful Spike/Dawn friendship. AGMHIS (and its sequels "Present Tense" and "Snippet") is the hottest, funniest, most heart-warming Spike/Joyce.
rahirah for "Necessary Evils" and "Follow the Yellow Brick Road". Barb's universe diverged from BtVS after The Gift and became something far greater than the show itself. NE is an alternate Season 6 that makes far more sense than did the real thing, and it is funnier and sweeter and also more tragic and scary. FTYBR is an amazing take on Spike/Dawn friendship that had me laughing until my pancreas shot out of my nose.
My own writing has been stalled for a couple of days; mainly because I've felt too drained on my return to work after a week off to do more than play with drabbles and memes. Tomorrow I have to get up early as we're having new windows and doors installed, so I can't do my usual all-night writing trick, and I'm not likely to have any peace to write during the day tomorrow. Sorry. However, the "ask any of my characters a question" meme that I included in my last post proved to be a useful exercise; it helped me do some ground work ready for future installments, so not really a waste of time. I'm still open for more questions. But please, no more questions for Paul the Walrus! He doesn't speak English and I'm worried that he'll want to answer by playing "the Star-Spangled Banner" on the xylophone.