Hanabata wins this one by miles. K cup is a reasonable size. Her other measurements are good too. It isn't all in the boobs. Hugeness everywhere is goodness everywhere.
Not sure what to make of the inverted nipples though. Is that source or simply something made up for decensoring?
One might settle for Hitamu's F cup if there was nothing better available, but it is kinda unimpressive, all considered. I mean with Hana and the receptionist walking around, she really is just middle-tier. Even the smallest of the girls I bothered with in Gal*Gun Double Peace was bigger around the chest than her.
As for the mages, they're just kids. Not even worth considering. Only paedophiles would even consider them.