Dropbox for Business Vs. OneDrive

hello all, 

So my client is on O365, and they have data in Dropbox, Google Drive, and OneDrive.  I would like to standardize a cloud storage solution for them.

They're very nimble in the sense that they don't have any servers on-prem, no AD setup, and aremostly Mac users with some using Office for Mac.

From a capacity perspective,  total of about 1.5TB with a feature growth to about 3TB over the next two years or so. (No one user will have more than 1TB  of data)

So, Dropbox or OneDrive?  

I should add that SharePoint isn't really an option.  Thoughts?