Other.
We saw too little of Angelus and Darla IMO. Dru and Spike, well she was insane, and it's hard to say wether she even loved him, specially with that running around with other demons thing. Wil and Xan, don't even get me started. Other great couple was Dru and Angelus, liked them a lot together, but I'm not voting for them either.
I think I'm voting for no couple at all.