Also I normally would prefer a girl like Yozora, but I don't like her that much, when she is so mean against Sena. Just my personal attitude of never making fun of your "friends" in public.
So I voted for Sena, although she is the kind of character I hardly consider attractive - too pretty and well-proportioned, too girly. But I find her cute when interacting with kodoka at home and such (and feel the aforementioned pity for her stupidity when acting with Yozora/Rika ) Can't really explain, but she is the most likeable and "normal" character for me.
Other girls are plain too young for my taste and too much cliche without depth. They also share the traits I dislike the most - too obedient and without self-awareness, too perverted and geeky, too lively and over-the-top. Though I agree wirh Sena here that Kobota is as cute as a button