Which one is more likely in canon?

I think the left one.
Well not so big though but still big(explains Rise's surprise when she saw her size in that check-up report)

And Naoto's subsequent reaction of snatching it off her and saying she was going to shred it. It wouldn't make sense for her to have that reaction to her small breasts being discovered since she uses sarashi to flatten her chest and wants people to think she's flat-chested anyway.