My personal favorite is onedrive. I've used them all. Onedrive, DropBox, Google Drive and Amazon SES. I basically just use Onedrive for my computer storage and backups and SES for my website storage and backups now.
Personally OneDrive. Mainly cause most of our local clients use it. However having used some of the others such as Dropbox and Google Drive. I still prefer OneDrive. Simple and gets what we need done for quick files on the go and share none essential/sensitive files.