Most:
Raelis Shai--She's exotic, experienced, independent, good-looking (and can cast Friends on top of that), and dang it, I dig her accent!
ToB NPC--Talk about having a forceful personality to interact with, and yet willing to let you be the boss! Plus there's the possibility of what the kids will be like, AND you can use him for a night-light! Just watch out for that 200 Piercing damage.
(If he was more interesting, I'd say Valygar. "So you're determined to be the last of your line, Mr. Corthala? Are you......sure about that?"
)
Least:
Pleasure Slave--Sure she's hot, sure she's naked, but her only desire is to serve my every whim? Please. Even Aerie is more interesting.
Korgan--Tie me up and rape me while I pull on your beard, you evil bastard. I want to smell your body odor!