Online backup services scan your hard drive for files worthy of protecting, encrypt them for security, and send them up to the company's online servers. Once your files are uploaded, you can access and restore your data from anywhere. Though there's some overlap, online backup services shouldn't be confused with cloud storage and file syncing services like Box, Dropbox, Google Drive, OneDrive, and SugarSync. Those services do store files in the cloud, but they aren't designed to automatically protect all important documents and media files, let alone system files. Their strategy is generally to sync just one folder with all its subfolders to the cloud, and in some cases, to offer online collaborative document editing. Many backup services offer folder-syncing capabilities, but few syncing services offer full-scale backup functionality.
Speed: Speed, in many cases, is far more dependent upon your broadband connection than that of the online service, though the geographical location of the storage and the equipment in between can make a significant difference. Check the location of the data servers if speed is important to you. Or, just give the trial a whirl and see if you can live with it.
SpiderOak's beauty is that it's a combination cloud syncing and storage service as well as a backup client all in one. Unlike some of the other services though, you'll have to pay for the storage you use. You get 2GB for free just for signing up, and you can get up to 10GB by referring friends. SpiderOak Plus nets you 100GB for $10/mo to use for syncing and backups, and every 100GB after that is another $10/mo. Plus, you can connect as many computers to any SpiderOak account as you want, so you're not paying by the system. You can read more about SpiderOak's plans here.
Since you're probably going to be paying for a backup service for years, cost is an important factor to consider. All the services rounded up here are subscription-based, but they partition their features and fees differently, so it's worth comparing plans closely before committing to one. Most construct pricing tiers based on the amount of cloud storage included, however, or by the number of devices you can use with an account. A few services offer permanent free accounts, but those plans impose paltry storage limits or restrict key features to the paid versions. Watch out for file-size upload limits as well.