I have used several “cloud” storage options. Currently, I use Dropbox pro (1TB for $99 a year), because it currently offers best bang for the buck, and has a fairly seamless Linux experience. Not open source, and I do have some mild concerns about security, but not enough to stop me from using it. I’ve found it to be the best at syncing across multiple computers and for collaborating with others. I currently used Dropbox to backup absolutely everything on all my of data - about 350gb. This includes all of my academic work and data sets, as well as photography and other personal things.
I have also a Google drive account for 15gb, but only use it for certain things. I use Google photos as a second “cloud” backup of my photos, but it limits to 12 megapixels or so. I upload all of my “good” photos to Flickr to back up and share in full resolution.
In the past I have used “spideroak” and “crash plan”. Both have Linux clients, and both are more foss-friendly than is Dropbox. Crash plan offers the most flexibility for backups, and is probably the most secure. It was more expensive than Dropbox for less storage, however, and is more difficult to sync across computers (you need to upgrade to the “business” version). Spideroak was good, but was difficult for collaboration via shared files and folders. If it was just me and one computer to back up, I might still be with one of these two services, but since I have other needs, it’s Dropbox for me for the foreseeable future.
Oh, and I used to use Ubuntu One cloud backup. I loved it. It was basically an open source Dropbox. But, alas, canonical killed it a few years back. 