Best fit, IMO:
Origins: Any Dalish, for the reasons expounded above. Though I think the Zevran romance makes more sense for a Dalish warden than any of the human romances, particularly if we're talking about a female warden. Iirc, the Dalish prefer their members to only reproduce with other elves, so having a baby with Morrigan seems like it would be done more out of practicality than love.
DA2: Any mage, romancing Anders, make Carver a warden, for obvious reasons. I suggest the Anders romance because his is arguably the romance most central to the plot.
Inquisition: Female Dalish rift mage who romances Solas. Not only is Solas's romance more tied in with critical plot developments than anyone else's in the series, but I think it's fitting that someone with the anchor becomes the sort of scholar who specialises in rift magics. Also, this inquisitor would take the "remove the vallaslin" option because it compliments Solas's background of freeing slaves.
But as for my favourite playthroughs!
Origins: Female Cousland who marries a hardened Alistair. Alistair's my favourite romance and I like the idea of the two who save Ferelden having a fairy tale ending. Also I think a hardened Alistair makes a better monarch than Anora. If any warden could become queen, I'd have the warden be a dwarf commoner because that's my favourite origin story.
DA2: Female warrior Hawke, romances Anders. I like Bethany better than Carver. Also, I've seen a fair few arguments about how was mage Hawke able to evade the templars in Act 2, and I agree that the reasons for Hawke's freedom are kind of glossed over.
Inquisition: Female Dalish rift mage who romances Cullen. Cullen's my favourite romance in that game. When I played Trespasser, I was torn between regret for not doing the most plot-relevant romance (Solas) and appreciation of the Cullen romance. I wish Solas would at least share the real meaning of the vallaslin with a non-romanced friend...