I find that many Cloud services offer encryption during transfer to the service and encryption at the destination. Dropbox does this too. Unfortunately, the keys used at the destination are available to Dropbox. What would make Dropbox unique is if it would offer Zero Knowledge encryption at the client. That way all files are encrypted at the client with the customer retaining the keys. Why is this important? There can be bugs during transfer even if encryption is used (remember the famous OOPS with caches on internet servers offering up unencrypted data?). Also, the government can force Dropbox to deliver user data (or it may be compromised by hackers).
Dropbox with Zero Knowledge Encryption would be a market leading solution that would drive a great preference over OneDrive, Google Drive and others. It would be the only way I would be comfortable putting my files on the cloud.