I'd really like Faith and Buffy together. . .
But if I had to choose between the two, definately Faith and Angel. They really have a lot of things going for them, he's a killer, she's a killer.
I think Angel had what it takes to help Faith. He understands her power, embraces it, and understands who she is. The darkness inside her corrupted her, much like it corrupted Angel. Once she had a taste of bad, she couldn't get enough. And that's essentially how Angel describes being a vampire. All about the kill, the thrill, the hunt. Thats realy what Faith was all about too.
Angel had a deeper understanding of what she was going through than anybody. And while I see how Faith and Spike could be together, Spike would in effect harm her more than help her. Spike revels in being bad, and as much as Faith would like us to think she likes it, she really hates that she's a killer. Spike accepts it, and loses no sleep over it. But Faith, no matter how many times she says she doesn't care, wants to be good, like Buffy. Angel gets that, because how many times has he said he wants to be good, for Buffy.
I may be completely rambling here, I'm just a wee bit off my rocker atm.
Fuffy all the way.