Thinking about it, a possibly crap hypothesis: I think one of the things which drives ones tastes in slash/femslash etc is the kind of interpersonal relationships we find engaging: if you like buddy-cop style relationships you probably are going to tend towards slash for example (or Bones :)) but might like Xena femslash. Just a thought, I don't know if it makes any sense.

Yeah, Susan/Talia is both really engaging and hard to imagine convincing happy endings for. (I've never tried any for that reason, so there is good stuff out there?)

My main femslash story is two characters who have definitely never met, so I understand the appeal :)