Favorite? Gretta. Sorry, but the big titty MILF is gonna be my favorite in every game, no exceptions. The netori + mommy kink angles just improve her appeal even further.
Second favorite? Serana. I just have a kink for putting arrogant nobility in their place in particular, so I'm looking forward to the inevitable moment when you deflower her.
Honorable mentions: Holly, who I like a lot as a character but more in a "I wanna hang out with her" way rather than as a sexual attraction. Gomira, who I also want to hang out with and it'd be really, really funny if the protagonist were to get pegged by her. Madeline, who is hot but not quite arrogant enough to trip my "I wanna knock her down a peg" kink. Dear Celestine, who wins the "biggest booba" prize but the whole premise of her actually being a nasty old woman who just looks hot due to magic glasses makes things too weird for her to score any higher. (Not weird enough for me to not do her, though.)
Least favorite: Anna. Sorry, she just doesn't appeal to me on any level, at least not in the tiny amount of content she's gotten thus far. The Anna update is the only one I'd seriously consider skipping to wait for the next one.