I'd go Dawn, Kennedy, and Adam.
I never had anything against Dawn and I think Michelle does a wonderful job portraying her. As others have noted, it's like she's not even acting. I loved her plot as the key, S5 had one of the best arcs IMO. So gripping!
As for Kennedy, I secretly like her (well, not so secretly anymore) for the same reasons a few of you other guys do. She's one of the only potentials to actually take their job as a...err...potential slayer seriously. She's got attitude, so what? At least she has personality, unlike most of the other girls.
And Adam, I thought, was an interesting villain, despite others throwing the word "boring" at him. It doesn't help he's sandwiched between two eccentric Big Bads in The Mayor and Glory. I liked his role, and thought the idea of a bio-mechanical demonoid was pretty cool. He had this sort of boyish innocence about him, but was also very sadistic. I wish he got more episodes than he did to flesh out his character a bit more.