Well, to a certain extent (some more than others), I'm a supporter of all those "ships" you mentioned, but the only one I personally see, assuming the Buffyverse goes on long enough of course, having a true "happily ever after" is Buffy and Angel. That being said, the theme of their relationship has always been no matter where they are, they are "forever", even if they aren't together. And I'm perfectly happy with that as well.
For me, and this is just a personal opinion of course, the other relationships you mentioned go like this: Buffy and Spike are two people who love each other but who don't work beyond passion. I kind of view Buffy and Angel as two people who are made for one another but can't be together and Buffy and Spike as two people are wrong for one another but love each other anyways (which in many ways is very realistic, and relatable). To me, they have an ending, and "Chosen" was it (and about as awesome and epic as you can get). And it's a happy one. However, by "The Girl in Question" Spike is about as true a champion as anyone else, and I'd have had no problem had he gone home with Buffy.
Buffy and Faith to me, well would be awesome 🙂D), but would be a short-lived affair. Really intense, really, really hot but ultimately not going to end well. Still, love to see it...
And Angel/Cordy, I look at that one as two people who were best friends, it grew into more but it just couldn't have worked. But if it had, they would have been happy together. Maybe more so than any of the other relationships, which in way also makes it the saddest.
But yeah, to me the other ones all have an end, and while it's not always what everyone else is happy with, I'm content with them. Buffy and Angel though, that one is forever to me. I don't know if we'll ever see them walk off into the sunset together or something like that, but I think the message is that one day, when the fighting is done, that's what will happen. Or at least, that's what I like to believe 🙂.