Edward Snowden has warned against the cloud storage service Dropbox which he says is "hostile to privacy," and called for more services to offer the 'zero knowledge' which have no decrypted access to user data.
Snowden pointed out that Dropbox had appointed former Secretary of State Condoleezza Rice to its board in April 2014.
For more sensitive files, I recommend using SpiderOak. While they only provide 2GB of space for free, that should be plenty of room for your more private files. If not, you can, of course, purchase more space from them.
All three of these services are Mac friendly. Microsoft's OneDrive is NOT Mac friendly, requiring file names and folders to follow Windows naming conventions.
Find the full article "Snowden: Dropbox is hostile to privacy, unlike 'zero knowledge' Spideroak" at The Guardian.