How strange that we humans should even be
attracted to creatures that are not our species. And yet it's true, some of the Trek aliens are undeniably attractive.
I voted Vulcans, Romulans (TOS), Cardassians and Bajorans. Each of these has attractive qualities, as do other species that I didn't pick.
Vulcans and Romulans (TOS variety) are physically attractive, in regards to their appearance and superior capabilities. I find the Vulcan stoicism and spirituality, as well as their striving for knowledge and truth, very attractive. Romulans seem so very passionate and bold, which is also attractive.
Something about the reptilian look about Cardassians is alluring in a way I can't quite put my finger on. And Bajorans are really cute, in my opinion, with their noses, and more beautiful in their spirituality.
Other races also have undeniably attractive qualities as well, of course.
Interesting topic to bring up.