Almost always I will marry Lucina, unless I'm doing a completionist support one (which I almost never do since I completed the supports that I wanted to do).
Even if I do marry someone other than Lucina,I never hand Lucina to anyone!
That, my friend...
... Actually, forget that bit about "my friend". That, person is the worst thing that you could do to Lucy. If she's unmarried by the end, then she gets her Single Ending, which is one of the saddest things in this game.
No, seriously. Read this:
Lucina disappeared after whispering these words to her infant self: "Yours will be a happy future." Did she journey to another land or back to her own time? ...No one knows for certain.
You would condemn her to this just because you want her to remain "your waifu" - while you yourself are fooling around with some other girl? For frick's sake, just marry her to somebody who isn't that philanderer Inigo.
That having been said, I will have Leeroy marry Lucina. Every time. No questions asked. OTP is OTP.
Chrom, every time. I'm honestly not fond of his and f!Robin's supports together, so I deliberately ignore their supports and go with the auto-triggered proposal scene at the end of Chapter 11 because I do like that scene. I like theirs best out of all of the potential wives' auto-triggered proposal dialogues, actually, and all of the cutscenes after that for the rest of the game hold a lot more weight when Robin is Chrom's wife. And in Future Past 3, if only Lucina survives to the end, the ensuing dialogue hits like a punch to the gut if Robin is her mother when Grima!Robin tells Lucina that she wishes that she could have had a normal life with Lucina.
And it's not just due to liking the Chrom-Robin dynamic, either. It's a lot because I hate it when anyone else is Lucina's mother. Like. I married him to Maribelle, Sumia, Olivia, and Sully once each just to have the marriage support dialogues recorded due to my completionist issues, but every single time that mother-daughter "reunion" scene played, my general reaction was GET AWAY FROM MY DAUGHTER, YOU WITCH. And then immediately reset the game and continued from my other "personal canon" save file.
The scene where Lucina tries to kill Robin is a lot more emotionally charged and potent when Robin is her mother, too.
With everyone else, I married them off based on how much I liked their supports together. :/ I just don't have the necessary callousness to go with eugenics, I'm afraid.
In short, I prefer the choices that make for (what I consider to be) the best story.