Muffy, because she's cute and easy to woo. I also like Witch Princess a lot.
I've never played the boy version, so my opinion is based on what I see in Cute. I'm sure I'd think differently about the other bacholorettes if I actually play the boy version.
Leia. She's different. All the other girls, except for Flora, could have been woo'd in AWL and FoMT, so I see no point in getting them again, unless you don't have either game, or you're getting a character you really like that just couldn't make a save file on your other game. (Due to having limited save slots).
I like all the special girls, now that I think about it. Flora, Keira, and Witch Princess come close. It's too bad I'd rather play as a girl, even though I don't get many bachelors to choose from. XD
I like Keira the best even though shes hard to marry her and takes alot of time. I like her because in my opinion shes pretty than the other girls and is a princess found sleeping in the mine.