I think that Xander is the only viable option for a long-haul relationship.

I've thought for a while that Buffy's best chances for a successful relationship were Spike and Xander.
I think she either needs someone superpowered, or someone who doesn't mind not being superpowered. (One of the many reasons Riley never had a chance.)

Mind you, I can't really see Buffy and Xander falling in love.
It's interesting: I'm happy for her to be in love with Angel, as long as they're not together. And I'm happy for Xander and Buffy to be together... as long as they're not in love!