I'm perfectly aware that Kasumi isn't as nice and angelic as people like to portray her as being. I still view her as being better than either Nabiki or Akane, and like I said, I have never seen much of the anime, and from what I've heard, that is a happy state of affairs for me, so Natsume and Kurumi are complete unknowns to me.
Despite what people say about Nabiki, the fact remains...she choose to blackmail Ranma, threatening to expose him to his mother, despite the fact that she knew his life was at stake. She didn't hesitate to rent out Ranma to the highest bidder when she was his fiancee. Five seconds after meeting poor orphan children, she was conning money out of them. She did not hesitate in the slightest to risk putting her entire family into permanent debt, and the only regret she expressed afterwards was she hadn't tried for more money...and if she had just been carried away, I would have expected her to have worried about it either sometime during or after, yet the thought that what she did was wrong never seems to have crossed her mind, or if it did, she didn't seem to care. She's perfectly willing to resort to emotional blackmail, as she demonstrated both during her engagement with Ranma, as well as during the whole incident with her lost ticket, and will happily wring as much advantage as possible out of your emotional turmoil. All in all, while I view her as being an amusing character, there's no way I would want anything to do with her as an individual.
Akane, on the other hand, annoys me because she lies to herself about her feelings, and violently strikes out, not to mention her general tendency to jump to conclusions, pounding first and asking questions later...frankly, I rarely like the tsundere archetype, and I certainly don't like Akane. While her lack of abilities in the domestic arts are somewhat troubling, if she wasn't so defensive about her lack of her ability in the domestic arts, or determined to keep on trying anyways...she's not as bad as some people like to portray her as being, but I still don't want to be married to her.
Kasumi, as I said, seems to be, to me at least, the most palatable choice of those choices presented. Though, as noted by others, I'd rather move out of Nerima with her and avoid the in-laws. Still, this is only on the assumption that I have to marry one...since, personally, at least in this particular stage in my life (I suppose it's plausible that at some time or another, I'll change my mind), I have little interest in marriage...much less to any of them. :mellow: