Natsumi's ending was my first pick as well because of that flashback of Kenichi's past and when his development began. Natsumi had such a major effect in his life that it would be a crime to not pick her route at all.
Sachi's ending was indeed touching, but you can't help it when the VN chooses Natsumi
Touka ended casually, while Ririko is still a major sadist.