I've read up to 9 volumes now, and my vote definitely goes for Leen now. Her being an ageless fairy is a huge plus for me (a trait which of course isn't without it's demerits though), but her more mature personality with a tinge of naughtiness to it is easily my favourite as well. She doesn't go too far with the teasing and isn't immune to being teased herself either thankfully. Her calling Touya "darling" seriously melts my heart (I just hope she says the same in the raws as well, like Kancolle's Kongou and Monmusu's Miia).
She has admitted to not loving Touya as much as the other girls, but that is only better in my view. While falling in love easily does not necessarily make that love any bit worse than love that slowly grows with time, but to me, at least in case with Smartphone, Leen's (currently) weaker love feels much more real and with the thought of it growing stronger with time, a much more rewarding form of love. In the end, love attained without effort just doesn't feel as satisfying.
Follow ups would be Cesca and Karen, if they were actual brides that is. As they are not, I'd say Yumina and Lu.
