I think I'd have to pick half of Sanae (not sure which half, though; probably her god half). She's a pretty sweet girl with knowledge of the outside world; I think her design is pretty neat; I like her ability to cause miracles; and I like how one of her spellcards is one of the few Windows-era Touhou references to Christianity. I also like how she's a foil to Reimu; while Reimu is more devoted to her miko tasks but can't use her channeling powers very well, Sanae has more of a connection to her shrine's deities but isn't a very good miko.
As for the other two Moriyas: Suwako is cool since she has earth powers and interesting since she subverts both the typical image of a goddess and the typical image of an Extra boss, but she kinda feels out of place due to that. And for Kanako... I'm sorry, Kanako supporters, but she doesn't really stand out to me, which is weird because I usually really like the final bosses of Touhou. I don't hate her, though; I just don't see much of a reason to like her. I really want to rectify that, though; a few good things I can say about her is that her shimenawa is cool and her onbashira are badass.