Yeah, Fukufics is probably to blame with the wave of girl!Ranma! Of course it is hard to find original good ideas before. Just that, I doubt girl!Ranma is the way to go. :no:
As for which one is hittable, of the character designs that I have seen, I'd probably go with Shampoo or even Nabiki. Heck, Ukyo isn't that bad looking either when she looks feminine. That being said, Kasumi is also nice on the eyes and her personality and attitude certainly helps in this field too.
That being said, I was never a 'huge' fan of Ranma's art. Decent, but well, I guess I'm more used to the more traditional 'anime' look of recent series.