I love them both, but my vote goes to Fredikins.
The episode Fredless has my favorite Amy Acker moment (well, besides "Please, Wesley, why can't I stay?" and "Would you like me to lie to you now?"):
"Well, sure. It's a story. Once upon a time, there was a girl who lived all alone in a horrible cave; so far from home it made her chest hurt. And every day in that horrible cave, the girl tried to figure out a way to escape. None of her plans ever succeeded, of course, and she'd almost given up hopin'. When one day, just like in a fairy tale, a handsome man rode up on a horse and saved her, and took her back to his castle. Now, you'd think that was the end, wouldn'tcha? Dumb old fairy tales and their 'happily ever after's. But see, the minute they got back to the castle, the handsome man went away again. And even though she didn't mean to, didn't want to, high up in that castle, the girl just built herself another cave; hoping he would save her again. But you can't save me this time, can you?"
Man, I relate to that in ways that are scary (certain behaviors--isolationism being one of mine, being rescued and then struggling to stop building yourself another cave). Ultimately, you've got to save yourself. I love that scene so much.
And Amy Acker is a wonderful actress. And the fact that Fred and Illyria were so different is a testament to her. "Because I look like her?"
Hopefully, Amy will get to shine as Whiskey on Dollhouse, too. In fact, it was her presence that actually made me the most excited about that show.