Who has the biggest breasts in the Naruto series?
Only Tsunade's measurements were revealed in the series (courtesy of Jiraiya). And I don't think the databooks include details like bust measurements. So the comparisons would be based on the appearance solely. Visual comparison isn't a good way of getting the right answer. 

But if you're looking for another character who has noticeably big oppai, there's Samui of Kumogakure: