I mainly use Google Drive and Dropbox and occasionally Amazon Cloud Drive, with them all being the free versions. I don’t use any cloud provider for backing up data, just mainly for syncing purposes. I have around 500GB of photos and video and besides the storage cost, just imagine trying to upload all that over my sluggish 384k DSL uplink…
Google Drive is very handy for OCR, e.g. I can upload PDF files and scanned images and it extracts the text.
My mobile phone came with a 2 year 25GB Dropbox subscription, so I use it for syncing the phone’s pictures and video with my PC. Once the subscription expires, I’ll likely switch it to Google Drive as it has a 15GB capacity.
I have a Kindle Fire, so the Amazon Cloud Drive is handy for syncing books to it, usually PDF files and DRM-free books I buy outside of Amazon.
As for what cloud service I’d avoid - That would be OneDrive. The business version is terribly resource intensive and also modifies files stored on it to add meta data. While the personal OneDrive doesn’t appear to be a resource hog, I still have certain issues with it - For example, it automatically downscales images synced to it (at least when I last tried it) and the PC version only syncs with Windows 7 and 8. The other cloud providers work on Windows Vista and even the obsolete Windows XP.
For backing up my photos and video, I stick with a combination of memory cards and external hard disks. Memory cards are so cheap that once a card fills up, I just get another, much like rolls of film.