Prime Universe Kira, without a doubt. Seeing as the two characters have (obviously) the same physical appearance, it has to come down to attitude. I've always thought Kira Nerys was sexually appealing, or at least in many ways fits my personal idea of a woman I'd like to build an intimate relationship with.
Because it is easier than typing up something equivalent again

, I'll re-post the nice things I said about Kira in the "Sexiest Star Trek Character" poll:
So much about her fits what I would be looking for in a "girlfriend": Spiritual, strong-willed, emotional, direct in her attitude and conduct with great complexity beneath it, hands-on, protective (in the "military officer" rather than the "parental" way), strong, dedicated to her people, physically appealing in a functional, natural way rather than through her makeup or clothes (the more "natural" a woman looks the more attractive I find her), in a position of authority and leadership...and still vulnerable in her way, enough so that I could be there for her as well, (I of course want my lover to need me as much as I her- I don't want to be some sort of clingy parasite

). Kira's instability and trauma makes me feel she could use someone to be there behind her, supporting her and healing her wounds as well as looking up to her. A woman raised in such trying and difficult circumstances but who becomes such a strong figure of the best in her people is appealing to me (the scene in the penultimate episode where she watches Damar rally the Cardassian civilians on the street is one of my favourite- how she just stands there, watching, realizing that Damar is for Cardassia what Shakaar is for Bajor- and that she was there behind them both, influencing and backing and supporting them both times. She is a hero to Bajor and to Cardassia. She has also helped Damar, who originally seemed to embody everything she hated (Cardassian thuggish militarism), become everything she admires (selfless heroism for the sake of one's people)). All in all, Odo was a lucky man. Still, there's still something that prevents her having quite the impact on me she could have. Maybe she's a little
too angry and traumatized in the early seasons (understandable given her upbringing and history, nothing wrong with it from a characterization viewpoint, but a little off-putting in regards to intimacy). I also think she could have used more of a sense of humour, as I find a lack of humour quite disappointing.
The Intendent, on the other hand, is not spiritual, is interested only in her own pleasures and seems to lack the strength of mind Kira is known for (certainly there is no moral strength in her, only desire). She shows no real complexity due to her fixation on her own pleasure, and spends so much time projecting a mask in order to manipulate others that she loses herself. She has no idea who she truly is beneath her title, or so I've always assumed. She's an act, an act designed to manipulate others and enhance her base desires wherever possible. Of particular importance in regards to "sexy", she seems to view sex and sexuality in terms of manipulation or simple gratification, whereas "our" Kira is clearly searching for a spiritual and intellectual companion. Our Kira is loyal to her friends, lovers, etc; the Intendent would sell her lover out for a chocolate bar. The Intendent also throws gratitious makeup and clothing over herself excessively to enhance her physical apperance (which as I said often detracts from a woman's attractiveness in my eyes), and is dedicated not to Bajor but to herself. Yes, she's also in a position of authority and leadership, but hardly one I can look up to and support (slaves labouring in the ore refinary is hardly a romantic backdrop in my eyes...). Ironically, she has a sense of humour, but not a healthy one...
The Intendent is not sexy at all. She tries to be, but she isn't (and that's in part why she isn't). She'd prefer manipulating her self-image and the image others have of her to actually behaving in a manner that would legitimately earn her appreciation. Of course, lots of people in the MU are like that...
Our Kira is sexier by a looooooong shot.
