And I'm not referering purely to esthetics (though it does count). Includes overall attitude and feel. Also count any incarnation where applicable (e.g. Uhura).
I'm sticking to major cast only for this, but feel free to use "other" for any recurrent / single appearance character of your choice.
Kira Nerys all the way. She's strong but sensitive and makes the little nose squiggle look great.