Dropbox desktop → Uploads only changed/new files, very efficient (block-level sync).

SharePoint / OneDrive desktop → Same as Dropbox, uploads only changes (block-level sync).

Google Drive desktop → Uploads only changed/new files, but always re-uploads the whole file when modified (less efficient for large files).

👉 For lots of small office files → all three are fine. 👉 For large files (backups, videos, databases) → Dropbox or OneDrive is better.