Maria has always been my favorite. She seems the most feminine to me, and I happen to like darker-colored hair and eyes, so she appeals to me most physically, too
Nerds are cute, and Maria is just adorable.
From a powergaming standpoint I believe Ann is the best, since she can feed your cows and sheep for you.
I least like Popuri. She's sort of like bubblegum - it might seem good at first, but pretty quickly you'll exhaust all the flavor it has, and then it's just a chore to keep around. She also doesn't do any animal-related stuff for you as a wife, and you should hopefully have a greenhouse by the time you get married, so she just doesn't do anything significant, either.
Elli and Karen I just sort of don't have an opinion on. I guess that's probably a bad thing