I agree with Ashley. I dislike couples that are completely unrealistic as far as the original plot goes. And I'm not refering to homosexual or heterosexual couples in particular. I'd hate a Sora and Riku coupling just as much as I'd hate a Yuffie and Ansem coupling.

So my obvious selection, aside from the Disney relations, would be Sora and Kairi, as that was most developed. Riku and Kairi would have worked except for the part about (SPOILER)Kairi's heart residing within Sora. I think that alone gives Sora and Kari the most believable bond.