I would say I would like to see a relationship between Rand and Elayne, if he absolutely has to have a relationship. I don't count what has transpired as an actual relationship. It's like they were ordered to have one, and hit certain milestones along the way without bothering to really relate to one another. Teenage courtship, check. Express mutual love, check. Make commitment, check. Make babies, check. With nothing in between. If the series was to be done over, that has the most potential for a relationship of his three love interests. Min is a joke, and Aviendha is not a sufficiently significant character to be a love interest for the main protagonist. Elayne is capable of operating on the same level as Rand, if not exactly his equal, and she is a fully fleshed out character with her own storyline and agenda, which makes a relationship between them more genuine, since they are two complete characters with interacting interests. Aviendha & Min simply do not have anything on the burner to bring any conflict (and with no conflict there is no story) to a relationship with Rand. Another alternative would have been to give Aviendha a more significant part. As the story is, she would be my preferred choice for Rand if he was to settle on a single relationship. I think as a person she has the most to offer him, with a unique perspective, even if most of her development and perspective has come about because she is sharing him.