Here's a run down of each character, from hottest to the least.
It's a null issue, Sarah Kerrigan, before being infested, is hotter. They even added her tits and nipples to the wire frame. She has a perfect tight littly body, huge breasts, nice long hair, and a cavalier attitude that beats all. She's hard to get, and has psychic powers. PSYCHIC POWERS! Talk about the stimulation that can provide.
The Dropship chick is definetly up there. It is of course assumed she has a great body, and she's a tomboy in my opinion. She's going to be willing to try out lots of new things and has a sexual lust that can't be beat.
The medic on the other hand, well, yep. She's the cute, shy girl. She probably won't try any new sexual positions. Also, how'd you like to think that, a few hours ago, this chick was patching up some bleeding guy or giving some old, wrinkly guy a sponge bath.
The Valkyrie chick is Russian, she's not hot. End of story.
Raszagal is several hundred years old, and of a different species. For all we know Protoss

eachother mentally... somehow.
The Zerg Queen is of a different species and isn't even humanoid. That's just sick.
Infested Kerrigan is the Queen

of the Universe. I suspect her privates have been sewn up, or she is a "miniature Sarlaac" down there. One attempt to have sex with her and BAM your

gets bitten off. Then she consumes your petrified body for energy, and casts Psionic Storm on your dog.