I use box.com and it work pretty well for me. however, I'm not syncing all my files and folders. Instead, I only sync the user data folder box created. Box doesn't let me add more folder to the list. You maybe able to hack it by creating symlinks, but its unsupported.
We started looking into using mega sync in the office. It has a big storage size in it free tier and heavy emphasis on encryption. Considering their old system was seized by the feds.
MEGA Review: 50GB of Free Cloud Storage and Bulletproof Security - BackupReview.com