I'm using Google Drive and Google Backup and Sync. I have 2TB of Drive cloud storage, though it seems I only need 1TB. A reduction at renewal time I think.....
OneDrive for all my regular files etc. For my hard drive, I can't bear to upload 500GB+ to the cloud, so I have an external hard drive that load everything onto once a month and then keep in my desk drawer at work.
I also have OneDrive O365 with 1TB. OneDrive has recently rolled out versioning across the consumer platform too which is great. Previously the major issue with synchronised oneline backups was that if a file became corrupt on your PC it would be mirrored and corrupted on your online stroage too. With versioning you can roll back to previous versions of the same file via the online interface. It really is a super feature:
But it's really only useful for a small number of files and isn't great if a whole suite of files become damaged or corrupt. And so I have two external hard drives - a 500GB one for docs and general stuff - and a 1TB one for my raw photos. Depending on my usage I would backup to these at least once a month - more frequently if I have a large number of photo dumps and always before I reformat my cameras memory card!
Actually I didn't realise you can do it directly from file explorer if you have the OneDrive app installed without having to go onto the online interface - handy! Easy single click to restore or download any previous versions.....
I use Currys KnowHow Cloud, have been recently rebranded as Cloud Backup. I found then to be the cheapest. And I use a a few devices, including a mobile.
DropBox Business (for sharing files/folders with clients)
Apple iCloud for all my Apple devices
Mega for large, encrypted file shares
I also have multiple HDD back-ups and Blu-Ray backups for client work, and a some client-provided OneDrive folders where they've preferred I don't put their stuff on my cloud services (but I then warn them that any backups are their responsibility).