I personally use dropbox the most as I have a pro-account there and it's just easy to upload files to people that way. Easy to send them a link to the content.
I often get files sent to me through wetransfer.com, it's more like a way to email large files.
Other than that, I use Google Drive too.
I use it to send large, video files to our customers that somehow have trouble downloading from our site. So dropbox is an alternative.