I liked 1897 Quentin with Beth. But the 1840 version of Quentin had good chemistry with Daphne.
Agree with those who thought Magda and Sandor made a good couple. Those two really seemed to have a shared history with each other; Grayson Hall and Thayer David played wonderfully off each other.
Whenever Nancy Barrett and John Karlen were paired, I though it really worked. So I like PT William H. Loomis and Carolyn Stoddard Loomis. You really felt that despite the bitterness and the booze, there was still a lot of love there. Melanie Collins and Kendrick Young also made a good couple, as did Leticia Faye and Desmond Collins.
Joshua and Naomi were great, really believable as a couple. So tragic that he doesn't really realize how much he loves her until it's too late.
As for would-be couples, I'm partial to Julia and Barnabas, but am unsure it ever would really have happened, had the show continued. And if it had, would it have worked?
Barnabas was kind of strange with everyone they paired him with romantically. Josette sort of worked, with Angelique there was a lot of heat, but utter madness too. He did seem to care for Victoria, but I can't see them really together. Forget about the Josette clones. And Barnabas with Roxanne? Was just creepy. Maybe he could have had something with Audrey the Leviathan vampire girl?
Always get a bit of a charge out of Julia with vampire Tom, but of course, that wasn't a relationship with a lot of real potential, was it?
Call me weird, but I thought that Cassandra and Tony Peterson were pretty sexy together, in a twisted sort of way. Would have been interesting if they'd gone further with that. Of course, Tony was good with Carolyn too.