i agree with SpikedBuffy. Buffy and Spike seemed more real to me than Buffy/Angel or Buffy/Riley. with those other two ships, they seemed to just jump right in at the deep end. Buffy mentions in 'Angel' that she's in love with Angel after having only known him a few weeks and kissing him for the first time the night before. i'm relly convinced that Bangel was too immature to last, at least on Buffy's part. she was 16 years old, and not emotionally mature enough for a proper relationship.
Briley, on the other hand, was more of a rebound thing and i knew it wouldn't last for more than a season.
Spuffy, however, had the time to mature. sure, they started out as enemies, but their relationship grew over the course of those first three years, giving Spike the time to realize how special Buffy was, and to truely fall in love with her. their relationship in S6 was a little selfish on Buffy's part. she was using him to make her feel something. but she realized how much she was hurting Spike by not loving him like he loved her, and so she ended it to stop them both hurting anymore.
by the time S7 came, Buffy found out how much Spike had gone through to show how much he loved her, and she explained to him in the ep 'First Date' that she needed him, by saying 'I'm not ready for you to not be here' showing that her feelings for him had changed dramatically since S2. by the time the series finale came, Buffy had realized herself that Spike was man she could imagine herself being with, and she turned down Angel (wasn't i jumping up and down when that happened!)
i still believe Buffy's last words to Spike were the truth, even though she didn't correct him when he told her she didn't. Spike told her to get out, to live the life she had always wanted, and by staying there to correct him, Buffy may well have died, and never get to live out Spike dying wish for her!
*phew* i think i've thuught about this FAR too much!