In comparing Arcs on a rating so far, my list would be like
1.
Kaoru (Just like most people said, the realistic feeling concerning her storyline)
2.
Ai (Just like Mycanid, unknown to what clicked for me for Ai, but it just did
)
3.
Haruka (You just gotta love Haruka's personality
)
4.
Sae (Cuteness was good.. But a very awkward setup in some senses)