Elle – The first thing that came to my mind here was Claire Bennet, though I wouldn't characterize it as direct answer to any of those questions except the last, and that's only when they're ever around each other. But they are narrative opposites, so it... comes up as the right answer? I'd tell her that her father would be a better one, but she wouldn't listen to me.

But, anyway, her issues with Claire pretty much all come down to jealousy one way or another: the belief that her own father would have liked Claire better (not really even because of her ability, but because she's sane, which just makes it worse), that Noah Bennet watched what happened to Elle but didn't do anything at all to help her, instead helping Claire (which is something her own father wouldn't do), and the notion that Claire's what she should have been but was cheated out of, since Bennet decided to help Claire because of what happened to her – after all, if Elle is what Claire would be had she been taken by the Company, Claire is what Elle would be like had she been saved from it.

But that's her answer. I don't think she's going to come around to mine until it's too late.

Caprica – Uh. I can't think of a lot of direct nemeses, maybe surprisingly enough. I'll just go with my head canon that the Sixes and the Ones generally dislike each other a lot.

Sharon – Boomer? And her inability to not screw up a landing.

Carla – ... well, when it comes down to it, no one is brave enough to be Carla's nemesis. Though it does bug the crap out of her when doctors talk down to her.

Emerson – THE NORWEGIANS. Er. Or things that have to complicate his life.