If you haven’t yet used cloud storage on your PC, you should give it a try. Problems with reliability have pretty much disappeared. Questions about privacy continue, and it’s a good idea to encrypt anything that’s supersensitive, but if you’re like most people, the convenience of having all of your cloud data available anywhere, anytime, goes a long way.
Everybody and his brother wants to offer you free cloud storage these days. They’re gambling that you’ll get hooked on the service and want to stay and pay. I’ve never gone over my limit with any of the services -- Dropbox (2GB free for personal use, unlimited business use for $12.50 per user per month), Microsoft’s OneDrive (5GB free for personal use, many other options), Google Drive (15GB free for personal use), Mega (50GB free), Box (10GB free) -- and I use them all, in various ways.
Thumbnail comparison: Dropbox syncs with your computer remarkably well; for all intents, it works exactly like a File Manager folder (see screenshot), offering solid security, easy operation, amazing reliability and integration with many programs (including Office).
The current version of OneDrive has all sorts of implementation and interface problems, reliability is a major concern, and Microsoft has already reneged on storage promises.
Google Drive space gets swallowed up by saved Gmail attachments, but the tools are best of breed. I use Google Drive for photos -- see my later recommendation.
Mega is excellent, supersecure, and somewhat in limited features, but getting better. Box rates as the sine qua non of corporate storage, but it’s limited for freeloaders.