My photos are all stored in iCloud because of the great integration between all my Apple devices. I have 2TB free from an old job but will have to switch to the 50gb for $0.99/month when that runs out. Also, I store my third-party password manager keychain in iCloud (I personally believe it has the best security).
The files I actively work on or have worked on semi-recently (school stuff, personal programming projects) are all in my Dropbox because I often need the files actually stored on my computer but also easily accessibly online from somewhere else. I only have 2.2 gigs of space, but it's fine because I'm usually storing plain text documents.
I use Google Drive for backups and any large files I don't need stored on my computer because I get unlimited space through university. This is usually an "upload and forget" type thing where I almost never go back and access the files, but still want them saved somewhere.
I use Youtube for saving video (I have a lot of drone footage). I upload hundreds of gigs of video to a private playlist. I don't need the original full quality videos, and would rather have ease of access from anywhere, so this works well.