I prefer One's Summer's Day. I think this song suits better for ending theme because after listening to it, we can feel emotional like what you endure the previous time. I think Nana's theme suits better for scene accompaniment. But, well, everyone has their own opinion.

I preferred the one summers day one because it gave off a reminiscent vibe while nanas theme showcased something really sad. They were actually both sad in their own way but to me each song gave off a kinda different vibe. Do you know what I mean?