I just don't see her with a macho warrior type, Faith with Spike are mates, Angel platonic life long friendship, all her previous relationships were unfulfilling, maybe even traumatic and not in the big love big pain way like what Buffy had. Faith has never felt loved ever, so to me part of Faith's journey besides redemption is discovering who she is, because having built a persona out of self defense mechanisms she doesn't really know.
Here is my case for why Anne is the best candidate, they are both young women with very similar backrounds but different enough, since their coping mechanisms and personalities are polar opposites and opposites attract. Anne can relate to the dark side just as well as Spike, Angel, Wood, but as a person with less issues of her own to work on. Faith can admire her (a big issue of hers with B was envy) what she wanted more then her life was to be loved by Buffy (platonically either way) except Buffy couldn't relate to Faith at that stage in her life (S6 definitely helped bury the hatchet) and was too young to help before it was to late. While Anne looks a little like Buffy, nurturing types like Anne are attracted to their protective testosterone driven opposites like Faith who "just wanted something to love" she would response positively to being needing in this protective way which is not there with the others. And being loved and admired by someone with such a good heart who could never hurt a fly also not there with the others, would boost her self esteem as someone being worthy of love.